Nobel Park S
Department of Biology, University of California, 90024, Los Angeles, CA, USA.
Laboratory of Biomedical and Environmental Sciences, University of California, 90024, Los Angeles, CA, USA.
Oecologia. 1984 Sep;64(1):1-7. doi: 10.1007/BF00377535.
An "environmental productivity index" based on physiological responses to three environmental variables was used to predict the net productivity of a common succulent perennial of the Sonoran Desert, Agave deserti, on a monthly basis. Productivity was also independently measured in the field from dry weight changes. The index was based on soil water availability, day/night air temperatures, and photosynthetically active radiation (PAR), which were individually varied in the laboratory and the effect on net CO uptake by the leaves determined. From monthly precipitation, temperature, and PAR at the field site together with the responses measured in the laboratory, an index (maximum value of unity) was assigned to each of these three environmental variables and their product was termed the environmental productivity index. This index indicates the fraction of maximal CO uptake expected in the field for each month (well-watered A. deserti assimilated 285 mmol CO m leaf area day at PAR saturation and optimal day/night temperatures of 25° C/15° C). The dry weight analysis was based on the monthly unfolding of new leaves from the central spike of the rosette and their seasonal increase in dry weight, which were determined in the field. The production of new leaves was highly correlated with the environmental productivity index (r=0.93), which in turn was highly correlated with the water status index (r=0.97). After correction for respiration by folded leaves, stem, and roots, plant productivity predicted by the average environmental productivity index (0.36) over a wet June-to-October period agreed within 4% with the productivity based on the conventional dry weight analysis. The net productivity of A. deserti over this 5-month period was 0.57 kg m ground area (5.7 Mg ha), a large value for a desert CAM plant. The environmental productivity index proposed here may provide a reliable means for predicting net productivity on a monthly basis, which may be particularly useful for species in relatively variable environments such as deserts.
基于对三种环境变量的生理反应构建的“环境生产力指数”，用于按月预测索诺兰沙漠常见多汁多年生植物——沙漠龙舌兰（Agave deserti）的净生产力。生产力还通过野外测量干重变化进行独立测定。该指数基于土壤水分有效性、昼夜气温以及光合有效辐射（PAR），在实验室中分别改变这些变量，并测定其对叶片净二氧化碳吸收的影响。根据野外站点的月降水量、温度和PAR，以及在实验室中测得的响应，为这三个环境变量分别赋予一个指数（最大值为1），它们的乘积即为环境生产力指数。该指数表明了每个月野外预期的最大二氧化碳吸收量的比例（水分充足的沙漠龙舌兰在PAR饱和且昼夜最佳温度为25°C/15°C时，每平方米叶面积每天同化285 mmol二氧化碳）。干重分析基于从莲座丛中心穗每月展开的新叶及其在野外测定的干重季节性增加。新叶的产生与环境生产力指数高度相关（r = 0.93），而环境生产力指数又与水分状况指数高度相关（r = 0.97）。在对折叠叶、茎和根的呼吸作用进行校正后，6月至10月湿润期的平均环境生产力指数（0.36）预测的植物生产力与基于传统干重分析的生产力相差在4%以内。这5个月期间沙漠龙舌兰的净生产力为每平方米地面面积0.57千克（5.7 Mg/公顷），对于沙漠景天酸代谢植物来说是一个很高的值。这里提出的环境生产力指数可能为按月预测净生产力提供一种可靠的方法，这对于沙漠等相对多变环境中的物种可能特别有用。
