Parrotia subaequalis, an endangered species endemic to eastern China, is on the national list of first-class key conservative plant. We investigated the difference of photosynthetic capacity among three diameter-classes of P. subaequalis trees, i. e. sapling, mid-sized tree and matured tree in Yixin, Jiangsu Province. The photosynthesis-related parameters and light response curves were measured using portable Li-6400 photosynthesis measuring system (Licor, USA). Our results showed that photosynthetic parameters of saplings, i.e. the maximal net photosynthesis rate (Pnmax), light saturation point (LSP), light compensation point (LCP) and dark respiration rate (R D), were significantly lower than those of mid-sized trees and matured trees. However, the specific leaf area (SLA) of saplings significantly was significantly greater. Photosynthetic physiological and morphological characteristics of saplings' leaves, including low LCP, RD and high SLA, demonstrated their great ability to tolerate shade. LSP of mid-sized trees was only half of that of matured trees, LCP of mid-sized trees was significantly higher than that of saplings, but not different from matured trees; Ranges of light utilization between LSP and LCP of mid-sized trees were extremely narrow. Furthermore, photosynthetically active radiation (PAR) above leaves of mid-sized trees was slightly higher than LCP but far below LSP; SLA of mid-sized trees was significantly lower than that of saplings and even slightly lower than that of matured trees. Based on the stepwise regression equation established between the net photosynthetic rate (Pn) and the environmental parameters, we found that PAR had the greatest contribution to Pn, and thus was the key limiting factors affecting photosynthetic capacity of P. subaequalis. PAR and air temperature (Ta) above leaves of saplings and mid-sized trees, which were under the shade of matured trees, were significantly lower than those above the leaves of matured trees. We concluded that saplings of P. subaequalis have flexible light-adaptation strategy in initial growing stage in shade. However, leaves of mid-sized trees show weak shade-tolerance in; low light conditions, which may contribute to the low numbers of mid-sized trees. Human intervention, such as selective removal and cutting of woods to create suitable canopy gaps may improve light condition and promote population regeneration of P. subaequalis.
|ジャーナル||Shengtai Xuebao/ Acta Ecologica Sinica|
|出版ステータス||出版済み - 2008|
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