Abstract
Rangelands play a critical role in the global carbon cycle. However, the eco-physiological mechanisms associated with the effects of grazing on leaf photosynthesis and soil respiration remain poorly understood. To examine the impacts of grazing on leaf photosynthesis and soil respiration, we measured the photosynthetic parameters of the dominant species (Trifolium repens) and the soil respiration in grazed and ungrazed rangelands in the Tianshan Mountains of China. We found that grazing reduced the daily maximum net photosynthetic rate and soil respiration rates by 35% and 15%, respectively. The photosynthetic quantum yield, dark respiratory rate, and water use efficiency of T. repens leaves were reduced in grazed plots by 33.3%, 69.2%, and 21.5%, respectively. Our results demonstrated that grazing reduced carbon assimilation while increasing soil respiration within the rangelands in the Tianshan Mountains.
Highlights
Rangelands contain 20–25% of the global terrestrial carbon within soil and vegetation, and play critical roles in both the global carbon cycle[1] and in the forage supply for livestock production worldwide[2]
To help address these gaps, we examined the photosynthesis of a dominant plant species and soil respiration in the Tianshan Mountain rangelands under grazed and ungrazed conditions
The photosynthetic capacity of T. repens leaves under grazed conditions was consistently lower than that of ungrazed conditions across a wide range of photosynthetic active radiation (PAR) (Table 1, Fig. 1)
Summary
Rangelands contain 20–25% of the global terrestrial carbon within soil and vegetation, and play critical roles in both the global carbon cycle[1] and in the forage supply for livestock production worldwide[2]. Research gaps, related to grazing effects on the photosynthetic features of plants and soil respiration, constrain the capacity to properly assess the effects of grazing on carbon assimilation and release in arid mountain rangelands. To help address these gaps, we examined the photosynthesis of a dominant plant species and soil respiration in the Tianshan Mountain rangelands under grazed and ungrazed conditions. We measured gas exchange and determined light response curves of T. repens leaves to assess carbon fixation, and soil respiration rate under grazed and ungrazed conditions in the Tianshan Mountains rangelands
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