Global maps and factors driving forest foliar elemental composition: the importance of evolutionary history.

Consistent information on the current elemental composition of vegetation at global scale and the variables that determine it is lacking. To fill this gap, we gathered a total of 30 912 georeferenced records on woody plants foliar concentrations of nitrogen (N), phosphorus (P) and potassium (K) from published databases, and produced global maps of foliar N, P and K concentrations for woody plants using neural networks at a resolution of 1 km2 . We used data for climate, atmospheric deposition, soil and morphoclimatic groups to train the neural networks. Foliar N, P and K do not follow clear global latitudinal patterns but are consistent with the hypothesis of soil substrate age. We additionally built generalized linear mixed models to investigate the evolutionary history effect together with the effects of environmental effects. In this comparison, evolutionary history effects explained most of the variability in all cases (mostly > 60%). These results emphasize the determinant role of evolutionary history in foliar elemental composition, which should be incorporated in upcoming dynamic global vegetation models.

The effect of global change on soil phosphatase activity.

Soil phosphatase enzymes are produced by plant roots and microorganisms and play a key role in the cycling of phosphorus (P), an often-limiting element in terrestrial ecosystems. The production of these enzymes in soil is the most important biological strategy for acquiring phosphate ions from organic molecules. Previous works showed how soil potential phosphatase activity is mainly driven by climatic conditions and soil nitrogen (N) and carbon. Nonetheless, future trends of the activity of these enzymes under global change remain little known. We investigated the influence of some of the main drivers of change on soil phosphatase activity using a meta-analysis of results from 97 published studies. Our database included a compilation of N and P fertilization experiments, manipulation experiments with increased atmospheric CO2 concentration, warming, and drought, and studies comparing invaded and non-invaded ecosystems. Our results indicate that N fertilization leads to higher phosphatase activity, whereas P fertilization has the opposite effect. The rise of atmospheric CO2 levels or the arrival of invasive species also exhibits positive response ratios on the activity of soil phosphatases. However, the occurrence of recurrent drought episodes decreases the activity of soil phosphatases. Our analysis did not reveal statistically significant effects of warming on soil phosphatase activity. In general, soil enzymatic changes in the reviewed experiments depended on the initial nutrient and water status of the ecosystems. The observed patterns evidence that future soil phosphatase activity will not only depend on present-day soil conditions but also on potential compensations or amplifications among the different drivers of global change. The responses of soil phosphatases to the global change drivers reported in this study and the consideration of cost-benefit approaches based on the connection of the P and N cycle will be useful for a better estimation of phosphatase production in carbon (C)-N-P models.

Increasing atmospheric CO2 concentrations correlate with declining nutritional status of European forests.

The drivers of global change, including increases in atmospheric CO2 concentrations, N and S deposition, and climate change, likely affect the nutritional status of forests. Here we show forest foliar concentrations of N, P, K, S and Mg decreased significantly in Europe by 5%, 11%, 8%, 6% and 7%, respectively during the last three decades. The decrease in nutritional status was especially large in Mediterranean and temperate forests. Increasing atmospheric CO2 concentration was well correlated with the decreases in N, P, K, Mg, S concentrations and the increase of N:P ratio. Regional analyses indicated that increases in some foliar nutrient concentrations such as N, S and Ca in northern Europe occurred associated with increasingly favourable conditions of mean annual precipitation and temperature. Crucial changes in forest health, structure, functioning and services, including negative feedbacks on C capture can be expected if these trends are not reversed.