Effects of plant species richness on 13C assimilate partitioning in artificial grasslands of different established ages

Abstract

Artificial grasslands play a role in carbon storage on the Qinghai–Tibetan Plateau. The artificial grasslands exhibit decreased proportions of graminate and increased species richness with age. However, the effect of the graminate proportions and species richness on ecosystem C stocks in artificial grasslands have not been elucidated. We conducted an in situ13C pulse-labeling experiment in August 2012 using artificial grasslands that had been established for two years (2Y), five years (5Y), and twelve years (12Y). Each region was plowed fallow from severely degraded alpine meadow in the Qinghai-Tibetan Plateau. The 12Y grassland had moderate proportions of graminate and the highest species richness. This region showed more recovered 13C in soil and a longer mean residence time, which suggests species richness controls the ecosystem C stock. The loss rate of leaf-assimilated C of the graminate-dominant plant species Elymus nutans in artificial grasslands of different ages was lowest in the 12Y grassland, which also had the highest species richness. Thus the lower loss rate of leaf-assimilated C can be partially responsible for the larger ecosystem carbon stocks in the 12Y grassland. This finding is a novel mechanism for the effects of species richness on the increase in ecosystem functioning.

Allocation and transfer of photosynthetic 13C in the vegetation‐soil system and its response to permafrost degradation

“…Studies have found that moderate grazing positively affects soil carbon input (Hafner et al, 2012). The carbon in wastelands is redistributed more proportionately and lasts longer than that in grasslands (Xu et al, 2017). Through studying the vegetation‐soil carbon allocation in different permafrost regions, we found that the 13 C excess in the wetlands exhibited a trend of leaf > root > soil (Figure 4), which is consistent with the results for cereals, forages, and poplars (Liu et al, 2019; Liu et al, 2020; Orgogozo et al, 2019).…”

“…Through studying the vegetation‐soil carbon allocation in different permafrost regions, we found that the 13 C excess in the wetlands exhibited a trend of leaf > root > soil (Figure 4), which is consistent with the results for cereals, forages, and poplars (Liu et al, 2019; Liu et al, 2020; Orgogozo et al, 2019). Another study conducted 13 C pulse experiments on artificial grasslands of different ages and found that the soil 13 C recovery rates were higher and the average residence time was longer in older grasslands, indicating that species richness has a greater impact on ecosystem carbon storage (Xu et al, 2017). The maximum 13 C excess of the plants in the different permafrost regions occurred in Mohe, and the migration to the roots was the largest (Figure 4).…”

“…Since 13 C is easily traceable, non‐radiative, and stable, it has been widely used for isotope labeling in field experiments in order to explore the transformation and decomposition of plant carbon and to reveal the turnover of carbon pools in different types of vegetation (Liu et al, 2020; Sarker et al, 2017). The isotopic compositions of the photosynthetic carbon in vegetation‐soil ecosystems remain stable for 2–21 days after labelling (Gao et al, 2015; Xu et al, 2017). The partitioning of the assimilated carbon in the vegetation‐soil system and the release of soluble organic matter into the soil are rapid processes (Liu et al, 2019).…”