Zhao Ping, Sun Gu-Chou, Ni Guang-Yan, Zeng Xiao-Ping
South China Botanical Garden, Guangzhou 510650, China.
Ying Yong Sheng Tai Xue Bao. 2013 Jan;24(1):49-56.
In this study, measurements were made on the leaf water potential (psi1), stomatal conductance (g(s)), transpiration rate, leaf area index, and sapwood area of mature Acacia mangium, aimed to understand the relationships of the leaf hydraulic conductance (K1) with the leaf water use and photosynthetic characteristics of the A. mangium in wet season (May) and dry season (November). The ratio of sapwood area to leaf area (A(sp)/A(cl)) of the larger trees with an average height of 20 m and a diameter at breast height (DBH) of 0.26 m was 8.5% higher than that of the smaller trees with an average height of 14.5 m and a DBH of 0.19 m, suggesting that the larger trees had a higher water flux in their leaf xylem, which facilitated the water use of canopy leaf. The analysis on the vulnerability curve of the xylem showed that when the K1 decreased by 50%, the psi1 in wet season and dry season was -1.41 and -1.55 MPa, respectively, and the vulnerability of the xylem cavitation was higher in dry season than in wet season. The K1 peak value in wet season and dry season was 5.5 and 4.5 mmol x m(-2) x s(-1) x MPa(-1), and the maximum transpiration rate (T(r max)) was 3.6 and 1.8 mmol x m(-2) x s(-1), respectively. Both the K1 and T(r max), were obviously higher in wet season than in dry season. Within a day, the K1 and T(r), fluctuated many times, reflecting the reciprocated cycle of the xylem cavitation and refilling. The leaf stomatal closure occurred when the K1 declined over 50% or the psi1 reached -1.6 MPa. The g(s) would be maintained at a high level till the K1 declined over 50%. The correlation between the hydraulic conductance and photosynthetic rate was more significant in dry season than in wet season. The loss of leaf hydraulic conductance induced by seasonal change could be the causes of the decrease of T(r) and CO2 gas exchange.
在本研究中，对成熟马占相思的叶片水势（ψ1）、气孔导度（g(s)）、蒸腾速率、叶面积指数和边材面积进行了测量，旨在了解雨季（5月）和旱季（11月）马占相思叶片水力导度（K1）与叶片水分利用及光合特性之间 的关系。平均树高20米、胸径（DBH）0.26米的大树边材面积与叶面积之比（A(sp)/A(cl)）比平均树高14.5米、DBH 0.19米的小树高8.5%，这表明大树叶木质部的水分通量更高，有利于冠层叶片的水分利用。对木质部脆弱性曲线的分析表明，当K1下降50%时，雨季和旱季的ψ1分别为-1.41和-1.55 MPa，旱季木质部空化的脆弱性高于雨季。雨季和旱季的K1峰值分别为5.5和4.5 mmol·m(-2)·s(-1)·MPa(-1)，最大蒸腾速率（T(r max)）分别为3.6和1.8 mmol·m(-2)·s(-1)。K1和T(r max)在雨季均明显高于旱季。在一天内，K1和T(r)多次波动，反映了木质部空化和再充盈的往复循环。当K1下降超过50%或ψ1达到-1.6 MPa时，叶片气孔关闭。在K1下降超过50%之前，g(s)将保持在较高水平。旱季水力导度与光合速率之间的相关性比雨季更显著。季节变化引起的叶片水力导度损失可能是T(r)和CO2气体交换下降的原因。
