Effects of Warming and N Deposition on the Physiological Performances of Leymus secalinus in Alpine Meadow of Qinghai-Tibetan Plateau

Warming and Nitrogen (N) deposition are key global changes that may affect eco-physiological process of territorial plants. In this paper, we examined the effects of warming, N deposition, and their combination effect on the physiological performances of Leymus secalinus. Four treatments were established in an alpine meadow of Qinghai-Tibetan plateau: control (CK), warming (W), N deposition (N), and warming plus N deposition (NW). Warming significantly decreased the photosynthetic rate (A(net)), stomatal conductance (g(s)), intercellular CO(2) concentration (C(i)), and transpiration rate (T(r)), while N deposition and warming plus N deposition significantly increased those parameters of L. secalinus. Warming significantly increased the VPD and L(s), while N deposition and warming plus N deposition had a significant positive effect. Warming negatively reduced the leaf N content, Chla, Chlb, and total Chl content, while N deposition significantly promoted these traits. Warming, N deposition, and their combination significantly increased the activity of SOD, POD, and CAT. Besides, warming and warming plus N deposition significantly increased the MDA content, while N deposition significantly decreased the MDA content. N deposition and warming plus N deposition significantly increased the Rubisco activity, while warming showed no significant effect on Rubisco activity. N deposition and warming plus N deposition significantly increased the Fv/Fm, ΦPSII, qP, and decreased NPQ, while warming significantly decreased the Fv/Fm, ΦPSII, qP, and increased NPQ. N deposition strengthened the relations between g(s), Chl, Chla, Chlb, Rubisco activity, and A(net). Under warming, only g(s) showed a significantly positive relation with A(net). Our findings suggested that warming could impair the photosynthetic potential of L. secalinus enhanced by N deposition. Additionally, the combination of warming and N deposition still tend to lead positive effects on L. secalinus.