Diurnal changes in the contents of organic acids, carbohydrates, and activities of two enzymes, phosphoenolpyruvate carboxylase (PEPC) and malate dehydrogenase (oxaloacetate-decarboxylating, NADP+) (ME), were compared between summer and winter conditions in a crassulacean acid metabolism (CAM) plant, pitaya. Preliminary experiments showed that pitaya’s PEPC required Mn2+ but not Mg2+, and exhibited maximum activity at pH 7.0, in contrast to the PEPCs of some other plants. Analyses of sap revealed that sucrose was the loading sugar in pitaya. In summer, the diurnal changes in the contents of organic acids and starch in pitaya were typical of starch-using CAM plants. In addition, no phosphoenolpyruvate carboxykinase (PEPCK) activity was detected, and high levels of starch, but not of hexose, accumulated. These results indicate that pitaya belongs to the ME-starch type among the four kinds of CAM plants. In winter, the levels of these substances (including sucrose) decreased, and there were no clear CAM-type diurnal changes. In particular, we did not detect malate accumulation during the night, degradation of malate during the day, or starch accumulation during the day. This may have resulted from decreased enzyme activities and lack of C3 photosynthesis during the day. Thus, since pitaya displays a reduced capacity for CO2 fixation in winter, it cannot store nutrients during this period.
A systematic survey of the collection of non-timber forest products (NTFPs) in several villages of the Koya people revealed the full scope of their trade in NTFPs which are linked to field-crop farming. Past research on NTFP trade among ethnic minorities in India emphasized the role of government procurement of NTFPs. However, out of the entire NTFP sales in the study villages, formal procurement by two government agencies accounted for only 32 %, whereas informal trade accounted for as much as 68 %. Palmyra (Borassus flabellifer) was the most important plant species. No government agency was involved in trade in any palmyra products. The NTFP trade has become a more reliable source of cash income than cash cropping. The Koya people appear to collect and sell NTFPs primarily as a way of raising funds to support their field-crop farming, which requires fertilizers and paid labor.
In the Bago Mountains of Myanmar, teak (Tectona grandis Linn.) reforestation using the taungya system has been in continuous operation for more than a century. Under this system, farmers who plant teak trees can cultivate intercrops between the rows of teak. In this region, secondary forests, especially bamboo-dominated forests, are usually slashed and burned to start a new taungya reforestation. To investigate the effect of the burning of bamboo-dominated forests on nutrient dynamics, changes in the soil nutrient status during the slash-and-burn and subsequent intercropping periods of taungya reforestation were examined quantitatively with particular focus on the effect of ash incorporation. After burning, approximately 85.1% of the aboveground biomass was lost and 4.2 t/ha of ash was produced. Although the loss of aboveground biomass was enormous, a significant increase in the amount of exchangeable K in the surface soil was observed. The nutrient dynamics in the soil were heavily influenced by the properties of the K-rich ash, which reflected the chemical composition of the original vegetation. The available P in the surface soil also increased due to a combination of the soil-heating effect and ash incorporation. The burning of bamboo-dominated forests confers certain advantages, including an increase in the amount of readily available essential nutrients such as K and P because bamboo ash contains a large amount of water-soluble K, and sufficient burning enhances the mineralization of organic P by the soil-heating effect.