Abstract
Many studies have reported that increasing atmospheric nitrogen (N) deposition broadens N:phosphorus (P) in both soils and plant leaves and potentially intensifies P limitation for plants. However, few studies have tested whether P addition alleviates N-induced P limitation for plant belowground growth. It is also less known how changed N:P in soils and leaves affect plant belowground stoichiometry, which is significant for maintaining key belowground ecological processes. We conducted a multi-level N:P supply experiment (varied P levels combined with constant N amount) for Glycyrrhiza uralensis (a N fixing species) and Pennisetum centrasiaticum (a grass) from a desert steppe in Northwest China during 2011–2013. Results showed that increasing P addition increased the belowground biomass and P concentrations of both species, resulting in the decreases in belowground carbon (C):P and N:P. These results indicate that P inputs alleviated N-induced P limitation and hence stimulated belowground growth. Belowground C:N:P stoichiometry of both species, especially P. centrasiaticum, tightly linked to soil and green leaf C:N:P stoichiometry. Thus, the decoupling of C:N:P ratios in both soils and leaves under a changing climate could directly alter plant belowground stoichiometry, which will in turn have important feedbacks to primary productivity and C sequestration.
Highlights
It is well known that anthropogenic activities, such as fossil fuel combustion, fertilizer use and intensive animal husbandry have produced a large number of nitrogen-containing compounds, which have resulted in increasing atmospheric nitrogen (N) deposition[1]
G. uralensis had relatively low belowground biomass but high rhizome to shoot ratio (RSR) compared with P. centrasiaticum (Fig. 1 and Table 2)
We found that the belowground biomass of G. uralensis increased with decreasing belowground N:P, soil C:P, soil N:P and green leaf C:P, while the belowground biomass of P. centrasiaticum improved with reducing soil N:P, green leaf C:P and green leaf N:P, respectively
Summary
It is well known that anthropogenic activities, such as fossil fuel combustion, fertilizer use and intensive animal husbandry have produced a large number of nitrogen-containing compounds, which have resulted in increasing atmospheric nitrogen (N) deposition[1]. The increasing P limitation would affect primary production and P cycling in P-limited ecosystems This raises two fundamental questions under N deposition: (1) how P addition affects P uptake and C:N:P stoichiometry in plants and (2) whether or not P addition alleviates N-induced P limitation for plant growth. The decoupling of C:N:P relationships in soils and leaves are supposed to affect the stoichiometric balance in plant belowground organs, which closely associates with key belowground ecological processes[11]. This conjecture has not been widely tested in terrestrial ecosystems, especially in desert steppe ecosystems. Our results will be helpful to identify the mechanism controlling elemental dynamics within soils and plants in desert steppe ecosystems
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