Uptake and recovery of soil nitrogen by bryophytes and vascular plants in an alpine meadow

Abstract

Due to their particular physiology and life history traits, bryophytes are critical in regulating biogeochemical cycles and functions in alpine ecosystem. Hence, it is crucial to investigate their nutrient utilization strategies in comparison with vascular plants and understand their responses to the variation of growing season caused by climate change. Firstly, this study testified whether or not bryophytes can absorb nitrogen (N) directly from soil through spiking three chemical forms of 15N stable isotope tracer.Secondly, with stronger ability of carbohydrates assimilation and photosynthesis, it is supposed that N utilization efficiency of vascular plants is significantly higher than that of bryophytes. However, the recovery of soil N by bryophytes can still compete with vascular plants due to their greater phytomass. Thirdly, resource acquisition may be varied from the change of growing season, during which N pulse can be manipulated with 15N tracer addition at different time. Both of bryophytes and vascular plants contain more N in a longer growing season, and prefer inorganic over organic N. Bryophytes assimilate more NH4+ than NO3-and amino acid, which can be indicated from the greater shoot excess 15N of bryophytes. However, vascular plants prefer to absorb NO3-for their developed root systems and vascular tissue. Concerning the uptake of three forms N by bryophytes, there is significant difference between two manipulated lengths of growing season. Furthermore, the capacity of bryophytes to tolerate N-pollution may be lower than currently appreciated, which indicates the effect of climate change on asynchronous variation of soil N pools with plant requirements.

A Non‐steady State Model Based on Dual Nitrogen and Oxygen Isotopes to Constrain Moss Nitrate Uptake and Reduction

“…These results suggest that moss NO 3 − uptake and accumulation is less a function of species identity, but it is rather more significantly influenced by environmental NO 3 − availability. This finding on moss NO 3 − uptake is consistent with that of tracer studies, which showed that the concentrations of applied 15 NO 3 − in mosses did not differ significantly between species, but they did differ significantly between doses of 15 NO 3 − applications or sites with different levels of atmospheric N deposition (Ayres et al, 2006; Wang et al, 2014; Wiedermann et al, 2009). In contrast, Wanek and Pörtl (2008) found that the kinetic constants of 15 NO 3 − uptake differed significantly between moss species, but not between bryophytes colonizing different microhabitats.…”

“…In this study, the average Φ soil values based on natural isotopes (equations and ) were 53 ± 13% (Figures 4a and 4b). Previously, the average fraction of soil‐derived N was determined to be 10% in a short‐term study (7 days) of mat‐forming mosses using labeled 15 N‐NO 3 − : 15 N‐NH 4 + (1:1) additions (Ayres et al, 2006), and the mean fractions of 15 N tracer recovery in the mosses from the 15 N‐NO 3 − spiked soils of an alpine meadow were 17–30% (Wang et al, 2014). These fractional contribution values cannot be directly compared due to differences in the methods used.…”

“…In a lowland tropical rainforest in Costa Rica, the bulk δ 15 N in epiphytic mosses suggests that N is taken up from the canopy soils (dead organic matter accumulated in branch crotches, on branches, and on boles; Wania et al, 2002). In alpine sites in Scotland and China, 15 N tracers added to soils were recovered in terricolous mosses although the proportions were relatively low (2–9% in Ayres et al, 2006; 17–30% in Wang et al, 2014). Nitrate is highly mobile and soil‐NO 3 − may enter the moss cells by diffusion, potentially through cotransport with positively charged ions (Raven et al, 1998).…”

“…This can be accomplished through their leptoids (phloem‐like cells) and hydroids (xylem‐like cells) (e.g., Polytrichum commune ; Reinhart & Thomas, 1981), or through capillary action (e.g., Racomitrium lanuginosum ; Jónsdóttir et al, 1995) and plasmodesmata (Wells & Brown, 1996). Thus, terrestrial mosses can absorb the N in soil substrates (Ayres et al, 2006; Wang et al, 2014). In a lowland tropical rainforest in Costa Rica, the bulk δ 15 N in epiphytic mosses suggests that N is taken up from the canopy soils (dead organic matter accumulated in branch crotches, on branches, and on boles; Wania et al, 2002).…”

Alterations to biological soil crusts with alpine meadow retrogressive succession affect seeds germination of three plant species

“…Most of these studies were performed in relatively stable ecosystems, whereas BSCs proceed from early to late succession stages over long time periods. BSCs make up an important component of all alpine meadow ecosystems (Wang et al 2014), but the BSC type and coverage changes with alpine meadow succession . BSCs in alpine meadows are a special case, because they are the result of intensive land use, especially overgrazing, and alpine meadow is fine-textured.…”