Par, Water, and Temperature Limitations on the Productivity of Cultivated Agave fourcroydes (Henequen)

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Abstract
Physiological responses to water status, temperature, and irradiation were studied in the laboratory and related to field values of the same parameters to predict dry matter productivity for A. fourcroydes, a Crassulacean acid metabolism (CAM) plant extensively cultivated in the Yucatan peninsula of Mexico. Low photosynthetically-active radiation (PAR), drought, or non-optimal temperatures reduced net CO2 uptake per unit leaf area and hence productivity. An environmental productivity index (EPI) was determined for each month using rainfall and air temperatures measured near the field site and simulated incident PAR corrected for cloudiness and adjusted to the leaf area index of the 3 plant age classes considered. EPI represented the product of the water status, temperature, and PAR indices, each of which had a value of unity when that factor was optimal or non-limiting. During the 1-yr study period, EPI was highly correlated with the number of leaves newly unfolding each month for all 3 age classes (average r2 = 0.85). Model calculations indicated that the traditional spacing between plants was nearly ideal and that irrigation would increase productivity only moderately in this subtropical region. The productivity of 6-yr-old plants, which were ready to be harvested commercially, was 1.60 kg dry wt m-2 yr-1. This is apparently the highest annual productivity reported for a CAM plant and is only slightly lower than for most C3 or C4 agricultural crops.