正常和环割条件下不同形态氮素添加对红椎幼苗光合特性的影响

采用盆栽试验和韧皮部环割方法研究了碳水化合物供应、氮素形态及其交互作用对红椎幼苗叶片光合特性的影响。无机氮源采用硝酸铵(AN)、铵态氮(NH_4~+-N)、硝态氮(NO_3~--N),有机氮源采用尿素(Urea)、精氨酸(Arg)和甘氨酸(Gly),氮素施用量均为10g N/m~2,处理时间为10 d。研究结果表明,环割、氮素形态及其交互作用均显著影响了红椎幼苗叶片的净光合速率(Pn);单一环割处理显著降低了红椎幼苗叶片Pn、气孔导度(Gs)、胞间CO_2浓度(Ci)、蒸腾速率(Tr)、相对叶绿素含量和CO2利用效率(CUE),但显著提高了叶片水分利用效率(WUE)和气孔限制值(Ls),其叶片Pn降低主要是由气孔限制和叶绿素含量降低所导致的。正常条件下,所有氮素形态处理均显著降低了红椎幼苗叶片的Pn、Gs、Ci和Tr,但显著升高了叶片Ls和WUE,其叶片Pn降低的主要原因是供氮过高引起的叶片气孔限制。正常条件下,除Arg处理外,其他氮素形态均显著升高了红椎幼苗叶片的CUE,其中以Gly处理的促进作用最大。环割条件下,3种有机态氮素的添加均显著缓解了单一环割处理对红椎幼苗叶片Pn的抑制作用,尤其以精氨酸最为明显,供应精氨酸的叶片Pn值从单一环割处理的强烈抑制中恢复到了对照水平,而无机态氮的供应均未显著改变这种抑制。结果表明短期碳水化合物供应的阻断会显著抑制红椎幼苗叶片的光合能力,适量供应精氨酸、甘氨酸和尿素等有机态氮会有效缓解这种抑制作用,其中以精氨酸的作用最为明显。

Effects of different nitrogen forms on foliar photosynthetic characteristics of Castanopsis hystrix seedlings under ungirdled and girdled conditions

The effects of carbohydrate supply, available nitrogen forms, and their interactions on the photosynthetic characteristics of Castanopsis hystrix seedlings were examined through manipulated pot experiments and phloem girdling. Three inorganic nitrogen sources (ammonia nitrate, AN; ammonium chloride, NH₄⁺-N; and potassium nitrate; NO₃^--N) and three organic nitrogen sources (Urea; arginine, Arg; and glycine, Gly), were applied at identical rates of 10g/m² for a 10d treatment. The carbohydrate supply, N forms, and their interactions had significant effects on the foliar net photosynthetic rate (Pn) of C. hystrix seedlings. Single girdling treatment significantly decreased leaf Pn, leaf stomatal conductance (Gs), leaf intercellular CO₂ concentration (Ci), leaf transpiration rate (Tr), relative chlorophyll content (RCC), and CO₂ use efficiency (CUE) of test seedlings, but it enhanced the leaf stomatal limitation values, as well as water use efficiency (WUE). The decreased Pn was mainly caused by leaf stomatal limitation, and reduction of foliar RCC. For non-girdling seedlings of C. hystrix, all treatments with N addition significantly decreased foliar Pn, Gs, Ci, and Tr, but increased foliar WUE and leaf stomatal limitation values. This is mainly due to stomatal limitation caused by high N loading. Moreover, all treatments with N addition significantly increased leaf CUE, except for the Arg addition treatment. In addition, the strongest stimulation effect on leaf CUE was caused by Gly addition. Correlation analysis indicated that Gs and Tr demonstrated significant correlations with leaf Pn, while Ci and RCC showed relatively weak correlations with leaf Pn. Additions of three organic N forms significantly reduced the inhibitory effect of the single girdling treatment on Pn of C. hystrix seedlings, with the most mitigated effect resulting from Arg addition. Due to the intense inhibitory effect of the single girdling treatment, the foliar Pn recovered to the control level upon Arg addition l, whereas all types of inorganic N additions did not have a significantly positive effect on the girdling-induced inhibition of Pn. Our results indicate that inhibition of carbohydrate supply could lead to reduction of the photosynthetic capacity of C. hystrix seedlings, while these inhibitory effects can be mitigated by organic N supply, such as Arg, Gly, and Urea, of which Arg had the greatest impact.