Foliar and soil concentrations and stoichiometry of nitrogen and phosphorous across European Pinus sylvestris forests: Relationships with climate, N deposition and tree growth

Sardans J., Alonso R., Janssens I.A., Carnicer J., Vereseglou S., Rillig M.C., Fernández-Martínez M., Sanders T.G.M., Peñuelas J. (2015) Foliar and soil concentrations and stoichiometry of nitrogen and phosphorous across European Pinus sylvestris forests: Relationships with climate, N deposition and tree growth. Functional Ecology. : 0-0.
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Doi: 10.1111/1365-2435.12541

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This study investigated the factors underlying the variability of needle and soil elemental composition and stoichiometry and their relationships with growth in Pinus sylvestris forests throughout the species' distribution in Europe by analysing data from 2245 forest stands. Needle N concentrations and N:P ratios were positively correlated with total atmospheric N deposition, whereas needle P concentrations were negatively correlated. These relationships were especially pronounced at sites where high levels of N deposition coincided with both higher mean annual temperature and higher mean annual precipitation. Trends towards foliar P deficiency were thus more marked when high N deposition coincided with climatic conditions favourable to plant production. Atmospheric N deposition was positively correlated with soil solution NO3- , SO42- , K+, P and Ca2+ concentrations, the soil solution NO3-:P ratio, total soil N and the total soil N:Olsen P ratio and was negatively correlated with soil Olsen P concentration. Despite these nutrient imbalances, during the period studied (1990-2006), N deposition was positively related with Pinus sylvestris absolute basal diameter (BD) growth, although only accounting for the 10% of the total variance. However, neither N deposition nor needle N concentration was related with relative annual BD growth. In contrast, needle P concentration was positively related with both absolute and relative annual BD growth. These results thus indicate a tendency of European P. sylvestris forests to store N in trees and soil in response to N deposition and unveil a trend towards increased nutrient losses in run-off as a consequence of higher soil solution N concentrations. Overall, the data show increasing ecosystem nutrient imbalances with increasingly limiting roles of P and other nutrients such as K in European P. sylvestris forests, especially in the centre of their distribution where higher levels of N deposition are observed. Thus, although the data show that N deposition has had an overall positive effect on P. sylvestris growth, the effect of continuous N deposition, associated with decreasing P and K and increasing N:P in leaves and in soil, may in the future become detrimental for the growth and competitive ability of P. sylvestris trees. © 2015 British Ecological Society.

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Foliar elemental composition of European forest tree species associated with evolutionary traits and present environmental and competitive conditions

Sardans J., Janssens I.A., Alonso R., Veresoglou S.D., Rillig M.C., Sanders T.G.M., Carnicer J., Filella I., Farre-Armengol G., Penuelas J. (2015) Foliar elemental composition of European forest tree species associated with evolutionary traits and present environmental and competitive conditions. Global Ecology and Biogeography. 24: 240-255.
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Doi: 10.1111/geb.12253

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Aim: Plant elemental composition and stoichiometry are crucial for plant structure and function. We studied to what extent elemental stoichiometry in plants might be strongly related to environmental drivers and competition from coexisting species. Location: Europe. Methods: We analysed foliar N, P, K, Ca and Mg concentrations and their ratios among 50 species of European forest trees sampled in 5284 plots across Europe and their relationships with phylogeny, forest type, current climate and N deposition. Results: Phylogeny is strongly related to overall foliar elemental composition in European tree species. Species identity explained 56.7% of the overall foliar elemental composition and stoichiometry. Forest type and current climatic conditions also partially explained the differences in foliar elemental composition among species. In the same genus co-occurring species had overall higher differences in foliar elemental composition and stoichiometry than the non-co-occurring species. Main conclusions: The different foliar elemental compositions among species are related to phylogenetic distances, but they are also related to current climatic conditions, forest types, drivers of global change such as atmospheric N deposition, and to differences among co-occurring species as a probable consequence of niche specialization to reduce direct competition for the same resources. Different species have their own 'fixed' foliar elemental compositions but retain some degree of plasticity to the current climatic and competitive conditions. A wider set of elements beyond N and P better represent the biogeochemical niche and are highly sensitive to plant function. Foliar elemental composition can thus be useful for representing important aspects of plant species niches. © 2014 John Wiley & Sons Ltd.

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Trees increase their P: N ratio with size

Sardans J., Penuelas J. (2015) Trees increase their P: N ratio with size. Global Ecology and Biogeography. 24: 147-156.
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Doi: 10.1111/geb.12231

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Aim: Phosphorus (P) tends to become limiting in ageing terrestrial ecosystems, and its resorption efficiency is higher than for other elements such as nitrogen (N). We thus hypothesized that trees should store more P than those other elements such as N when tree size increases and that this process should be enhanced in slow-growing late-successional trees. Location: Catalan forests. Methods: We used data from the Catalan Forest Inventory that contains field data on the P and N contents of total aboveground, foliar and woody biomasses of the diverse mediterranean, temperate and alpine forests of Catalonia (1018 sites). We used correlation and general linear models to analyse the allometric relationships between the nutrient contents of different aboveground biomass fractions (foliar, branches and stems) and total aboveground biomass. Results: Aboveground forest P content increases proportionally more than aboveground forest N content with increasing aboveground biomass. Two mechanisms underlie this. First, woody biomass increases proportionally more than foliar biomass, with woody biomass having a higher P:N ratio than foliar biomass. Second, the P:N ratio of wood increases with tree size. These results are consistent with the generally higher foliar resorption of P than of N. Slow-growing species accumulate more total P aboveground with size than fast-growing species, mainly as a result of their large capacity to store P in wood. Main conclusions: Trees may have developed long-term adaptive mechanisms to store P in biomass, mainly in wood, thereby slowing the loss of P from ecosystems, reducing its availability for competitors and implying an increase in the P:N ratio in forest biomass with ageing. This trend to accumulate more P than N with size is more accentuated in slow-growing, large, long-lived species of late successional stages. In this way they partly counterbalance the gradual decrease of P in the soil. © 2014 John Wiley & Sons Ltd.

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Potassium: A neglected nutrient in global change

Sardans J., Penuelas J. (2015) Potassium: A neglected nutrient in global change. Global Ecology and Biogeography. 24: 261-275.
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Doi: 10.1111/geb.12259

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Aim: Potassium (K) is the second most abundant nutrient in plant photosynthetic tissues after nitrogen (N). Thousands of physiological and metabolic studies in recent decades have established the fundamental role of K in plant function, especially in water-use efficiency and economy, and yet macroecological studies have mostly overlooked this nutrient. Methods: We have reviewed available studies on the content, stoichiometry and roles of K in the soil-plant system and in terrestrial ecosystems. We have also reviewed the impacts of global change drivers on K content, stoichiometry and roles. Conclusions: The current literature indicates that K, at a global level, is as limiting as N and phosphorus (P) for plant productivity in terrestrial ecosystems. Some degree of K limitation has been seen in up to 70% of all studied terrestrial ecosystems. However, in some areas atmospheric K deposition from human activities is greater than that from natural sources. We are far from understanding the K fluxes between the atmosphere and land, and the role of anthropogenic activities in these fluxes. The increasing aridity expected in wide areas of the world makes K more critical through its role in water-use efficiency. N deposition exerts a strong impact on the ecosystem K cycle, decreasing K availability and increasing K limitation. Plant invasive success is enhanced by higher soil K availability, especially in environments without strong abiotic stresses. The impacts of other drivers of global change, such as increasing atmospheric CO2 or changes in land use, remain to be elucidated. Current models of the responses of ecosystems and carbon storage to projected global climatic and atmospheric changes are now starting to consider N and P, but they should also consider K, mostly in arid and semi-arid ecosystems. © 2015 John Wiley & Sons Ltd.

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Shifts in the elemental composition of plants during a very severe drought

Urbina I., Sardans J., Beierkuhnlein C., Jentsch A., Backhaus S., Grant K., Kreyling J., Penuelas J. (2015) Shifts in the elemental composition of plants during a very severe drought. Environmental and Experimental Botany. 111: 63-73.
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Doi: 10.1016/j.envexpbot.2014.10.005

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Diverse plant functions (e.g., growth, storage, defense and anti-stress mechanisms) use elements disproportionally. We hypothesized that plants growing under different abiotic and biotic conditions would shift their elemental compositions in response to a very severe drought. We tested this hypothesis by investigating the changes in foliar stoichiometry and species composition from a very severe drought. We also tested the effects of previous droughts (acclimation) on this response. Different species growing in the same community responded more similarly to a very severe drought than did individual species growing in different communities. The stoichiometric shifts were thus more community-dependent than species-dependent. The results also suggested that plants grown in monoculture were less stoichiometrically plastic during the drought than plants grown in a more diverse community. Previous exposure to long-term drought treatments in the same communities did not significantly affect the stoichiometric shifts during the new drought. Differential use of resources may have been responsible for these responses. Monocultured plants, which used the same resources in similar proportions, had more difficulty avoiding direct competition when the resources became scarcer. Moreover, each species tested had a particular elemental composition in all communities and climatic treatments. The differences in foliar elemental compositions were largest between plant functional groups (shrubs and grasses) and smallest among species within the same functional group. Global principal components analyses (PCAs) identified a general tendency for all species, independently of the community in which they grew, toward lower concentrations of K, N, P, Mg and S, and to higher concentrations of C and Fe as the drought advanced. This study has demonstrated the utility of analyses of differences and shifts in plant elemental composition for understanding the processes underlying the responses of plants to changes in biotic and abiotic environmental conditions. © 2014.

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Rice straw incorporation affects global warming potential differently in early vs. late cropping seasons in Southeastern China

Wang W., Lai D.Y.F., Sardans J., Wang C., Datta A., Pan T., Zeng C., Bartrons M., Penuelas J. (2015) Rice straw incorporation affects global warming potential differently in early vs. late cropping seasons in Southeastern China. Field Crops Research. 181: 42-51.
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Doi: 10.1016/j.fcr.2015.07.007

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Paddy fields are a major global anthropogenic source of methane (CH4) and nitrous oxide (N2O), which are very potent greenhouse gases. China has the second largest area under rice cultivation, so developing valid and reliable methods for reducing emissions of greenhouse gases while sustaining crop productivity in paddy fields is of paramount importance. We examined the effects of applying straw, a residual product of rice cultivation containing high amounts of carbon and nutrients, to rice crops during both an early crop season (5 April - 25 July 2012) and a late crop season (1 August - 6 November 2012) on CH4 and N2O emissions in a subtropical paddy field in southeastern China. CH4 fluxes had two seasonal peaks, on 5 May and 28 June, in the early crop but only one peak, on 13 August, in the late crop, which could be attributed to the lower temperatures after the final tillering stage in the late crop. Straw application significantly increased mean CH4 cumulative production (gm-2) relative to the control in the late crop (37.3 vs. 8.34mgm-2, P 0.05). The application of straw significantly increased N2O cumulative production relative to the control in the late crop (75.9 vs. 43.4μgm-2h-1) but decreased N2O cumulative production by over 43% in the early crop (15.60 vs. 27.27μgm-2h-1) (P

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Effects of steel slag application on greenhouse gas emissions and crop yield over multiple growing seasons in a subtropical paddy field in China

Wang W., Sardans J., Lai D.Y.F., Wang C., Zeng C., Tong C., Liang Y., Penuelas J. (2015) Effects of steel slag application on greenhouse gas emissions and crop yield over multiple growing seasons in a subtropical paddy field in China. Field Crops Research. 171: 146-156.
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Doi: 10.1016/j.fcr.2014.10.014

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Asia is responsible for over 90% of the world's rice production and hence plays a key role in safeguarding food security. With China being one of the major global producers and consumers of rice, achieving a sustainable balance in maximizing crop productivity and minimizing greenhouse gas emissions from paddy fields in this country becomes increasingly important. This study examined the effects of applying steel slag, a residual product derived from the steel industry, on crop yield and CH4 and N2O emissions over multiple growing seasons in a Chinese subtropical paddy field. Average CH4 emission was considerably higher during the periods of rice crop growth compared to that during the periods of fallowing and vegetable crop growth, regardless of the amount of steel slag applied. When compared to the controls, significantly lower mean emissions of CH4 (1.03 vs. 2.34mgm-2h-1) and N2O (0.41 vs. 32.43μgm-2h-1) were obtained in plots with slag addition at a rate of 8Mgha-1 over the study period. The application of slag at 8Mgha-1 increased crop yields by 4.2 and 9.1% for early and late rice crops, respectively, probably due to the higher availability of inorganic nutrients such as silicates and calcium from the slag. Slag addition had no significant effect on the concentrations of heavy metals in either the soil or the rice grains, although a slight increase in the levels of manganese and cobalt in the soil and a decrease in the levels of manganese and zinc in the rice grains were observed. Our results demonstrate the potential of steel slag as a soil amendment in enhancing crop yield and reducing greenhouse gas emissions in subtropical paddy fields in China, while posing no adverse short-term impacts on the concentrations of heavy metals in the soil or the rice grains. However, long-term implications of this management practice and the cost/benefit remain unknown, so further studies to assess the suitability at large scale are warranted. © 2014 Elsevier B.V.

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Agricultural land use decouples soil nutrient cycles in a subtropical riparian wetland in China

Wang W., Wang C., Sardans J., Min Q., Zeng C., Tong C., Penuelas J. (2015) Agricultural land use decouples soil nutrient cycles in a subtropical riparian wetland in China. Catena. 133: 171-178.
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Doi: 10.1016/j.catena.2015.05.003

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We examined the impact of human changes in land use on the concentrations and stoichiometric relationships among soil carbon (C), nitrogen (N), phosphorus (P) and potassium (K) in a Phragmites australis riparian wetland (Minjiang River estuary, China). We compared a natural (unaltered) wetland with five altered land uses: intertidal mudflat culture and vegetable, flower, fruit and rice cultivations. All these land uses decreased C, N and K soil concentrations relative to those in the P. australis wetland. The close relationship between total soil C and N concentrations, under all land uses, suggested that N was the most limiting nutrient in these wetlands. The lower N concentrations, despite the use of N fertilizers, indicated the difficulty of avoiding N limitation in the agricultural land. Croplands, except rice cultivation, had lower soil N:P ratios than the original P. australis wetland, consistent with the tendency of favoring species adapted to high rates of growth (low N:P ratio). The release of soil C was less and the soil C:N and C:P ratios higher in the natural P. australis riparian wetland than in the croplands, whereas C storage was more similar. The levels of soil C storage were generally opposite to those of C release, indicating that C release by respiration was the most important factor controlling C storage. Cropland soil management promotes faster nutrient and C cycles and changes in soil nutrient stoichiometry. These impacts can further hinder the regeneration of natural vegetation by nutrient imbalances and increase C-cycling and C emissions. © 2015 Elsevier B.V.

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Flood regime affects soil stoichiometry and the distribution of the invasive plants in subtropical estuarine wetlands in China

Wang W., Wang C., Sardans J., Tong C., Jia R., Zeng C., Penuelas J. (2015) Flood regime affects soil stoichiometry and the distribution of the invasive plants in subtropical estuarine wetlands in China. Catena. 128: 144-154.
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Doi: 10.1016/j.catena.2015.01.017

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Projections of climate change impacts over the coming decades suggest that rising sea levels will flood coastal wetlands, moving the range of wetlands inland from the current coastline. The intensity of flooding in wetland areas will thus increase, with corresponding impacts on soil properties and coastal ecosystems. We studied the impacts of two levels of water inundation on the concentration and stoichiometry of soil carbon, nitrogen, phosphorus and sulfur in areas dominated by the native C3 species Scirpus triqueter L., the native C4 species Cyperus malaccensis var. brevifolius Boecklr. and the invasive Gramineae C3 species Phragmites australis (Cav.) Trin. ex Steud in the Shanyutan wetland areas of the Minjiang River estuary in China. Comparison of the communities dominated by these three species in high- and low-water flood habitats showed that flooding enhanced anaerobiosis and salinity and altered the carbon and nitrogen plant-soil cycles. Higher flooding favored the invasive species more than the two native species. The invasive P. australis accumulated more carbon (65% increase in aboveground biomass), and took up more nitrogen under high flooding than did C. malaccensis and S. triqueter. The more conservative use of soil resources, particularly the limiting nutrient N, appeared to underlie the higher capacity of the invasive species to tolerate higher flooding intensity. Increases in flooding may thus enhance the success and expansion of the invasive P. australis to the detriment of the native plant species in these Chinese wetlands. © 2015 Elsevier B.V.

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Impact of Plant Invasion and Increasing Floods on Total Soil Phosphorus and its Fractions in the Minjiang River Estuarine Wetlands, China

Wang W.-Q., Sardans J., Zeng C.-S., Tong C., Wang C., Peñuelas J. (2015) Impact of Plant Invasion and Increasing Floods on Total Soil Phosphorus and its Fractions in the Minjiang River Estuarine Wetlands, China. Wetlands. : 0-0.
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Doi: 10.1007/s13157-015-0712-9

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Plant invasion and increased flooding intensity projected by climate change models can change the soil capacity of marine wetland to store P. This is a key question to the nutrient balances and eutrophication processes of coastal areas, especially in China coastal area that is receiving the freshwaters of a country in fast economical developing process. We studied the impact of changes in flooding intensity and plant invasion on total soil-P concentrations in the Minjiang River estuarine wetland. Flooding had a weak positive effect on soil P-fractions concentrations, but this effect was largely counteracted by the negative effect of salinity. Soil clay concentration and pH, both of which were related more with species community composition than with flooding intensity, were directly related to the P-fraction concentrations. The replacement of the native mangrove community by the invasive plant Phragmites australis was related to a decrease in the soil capacity to store P. A suitable management to maintain this wetland area in optimum conditions to act as a natural eutrophication buffer should tend to favor mangrove communities in the new areas that reach more than 220 days y-1 of flooding, and a combination of the three tall-grasses communities below this level of flooding. © 2015 Society of Wetland Scientists

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