Faculty of Forestry and Nature Conservation, University of Chile, PO Box 9206, Santiago, Chile.
Manaaki Whenua - Landcare Research, PO Box 69054, Lincoln 7640, New Zealand.
Tree Physiol. 2024 Aug 3;44(8). doi: 10.1093/treephys/tpae087.
We tested an approach to estimate daily canopy net photosynthesis, A, based on estimates of transpiration, E, using measurements of sap flow and water-use efficiency, ω, by measuring δ13C in CO2 respired from shoots in the canopies of two conifers (Podocarpaceae) native to New Zealand. The trees were planted in adjacent 20-year-old stands with the same soil and environmental conditions. Leaf area index was lower for Dacrycarpus dacrydioides D.Don in Lamb (1.34 m2 m-2) than for Podocarpus totara G.Benn. ex D.Don var. totara (2.01 m2 m-2), but mean (± standard error) stem diameters were the same at 152 ± 21 mm for D. dacrydioides and 154 ± 25 mm for P. totara. Over a 28-day period, daily A (per unit ground area) ranged almost five-fold but there were no significant differences between species (mean 2.73 ± 1.02 gC m-2 day-1). This was attributable to higher daily values of E (2.63 ± 0.83 mm day-1) and lower ω (1.35 ± 0.53 gC kg H2O-1) for D. dacrydioides compared with lower E (1.82 ± 0.72 mm day-1) and higher ω (1.90 ± 0.77 gC kg H2O-1) for P. totara. We attributed this to higher nitrogen availability and nitrogen concentration per unit foliage area, Na, and greater exposure to irradiance in the D. dacrydioides canopy compared with P. totara. Our findings support earlier observations that D. dacrydioides is more adapted to sites with poor drainage. In contrast, the high retention of leaf area and maintaining low rates of transpiration by P. totara, resulting in higher water-use efficiency, is an adaptive response to survival in dry conditions. Our findings show that physiological adjustments for two species adapted to different environments led to similar canopy photosynthesis rates when the trees were grown in the same conditions. We demonstrated consistency between whole-tree and more intensive shoot-scale measurements, confirming that integrated approaches are appropriate for comparative estimates of carbon uptake in stands with different species.
我们测试了一种基于蒸腾量 E 的估算方法来估算冠层净光合速率 A，该方法使用树干液流和水分利用效率 ω 的测量值，通过测量冠层中两种新西兰原产针叶树（罗汉松科）的叶片释放的 CO2 中的 δ13C 来估算。这两种树木种植在相邻的 20 年生林分中，具有相同的土壤和环境条件。在 Lamb 的戴科拉卡帕克斯（Dacrycarpus dacrydioides D.Don）的叶面积指数（LAI）较低（1.34 m2 m-2），而托塔拉罗汉松（Podocarpus totara G.Benn. ex D.Don var. totara）的 LAI 较高（2.01 m2 m-2），但平均（±标准误差）茎直径相同，为 152±21mm 用于 D. dacrydioides 和 154±25mm 用于 P. totara。在 28 天的时间里，单位地面面积的日 A（每单位地面面积）范围几乎相差五倍，但种间没有显著差异（平均 2.73±1.02 gC m-2 day-1）。这归因于戴科拉卡帕克斯（D. dacrydioides）较高的日蒸腾量（2.63±0.83mm day-1）和较低的水分利用效率（1.35±0.53gC kg H2O-1），而较低的蒸腾量（1.82±0.72mm day-1）和较高的水分利用效率（1.90±0.77gC kg H2O-1）用于 P. totara。我们将这归因于较高的氮可用性和单位叶面积的氮浓度 Na，以及戴科拉卡帕克斯冠层中对光照的更高暴露率，与 P. totara 相比。我们的发现支持早先的观察结果，即 D. dacrydioides 更适应排水不良的地点。相比之下，P. totara 保持较低的蒸腾速率和较高的水分利用效率，从而保留较高的叶面积，这是对干旱条件下生存的适应性反应。我们的研究结果表明，适应不同环境的两个物种的生理调整导致当树木在相同条件下生长时，冠层光合作用速率相似。我们展示了全树和更密集的枝条尺度测量之间的一致性，证实了综合方法适用于不同物种林分中碳吸收的比较估算。
