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In this study, the compressive strength, water absorption, and thermal conductivity of palm oil fuel ash (POFA) lightweight geopolymer concrete (LWGC) incorporating high-calcium fly ash (FA) and Portland cement (PC) are reported. The POFA was replaced by FA or PC at the dosages of 60% by weight of binder. The wet density of POFA-based LWGC incorporating FA and PC was designed at 1000 kg/m3, based on ASTM C796. Test results found that the incorporation of FA and PC in POFA-based LWGC could significantly improve the strength development of LWGC. The reactive Ca ions could react with SiO2 from POFA, leading to the additional formation of reaction products within the LWGC. The thermal conductivity of LWGC showed an excellent option for reducing the temperature change in the wall section during a day. It was positive effects on the building's electricity cost. A combination of POFA-based LWGC with PC met the 28-day strength and water absorption requirements as per TIS.2601-2556. Therefore, POFA-based LWGC incorporated with PC can be used as the non-load-bearing brick masonry units.

Shoots of the tropical latex-producing tree Hevea brasiliensis (rubber tree) grow according to a periodic pattern, producing four to five whorls of leaves per year. All leaves in the same whorl were considered to be in the same leaf-age class, in order to assess the evolution of photosynthesis with leaf age in three clones of rubber trees, in a plantation in eastern Thailand. Light-saturated CO2 assimilation rate ( Amax) decreased more with leaf age than did photosynthetic capacity (maximal rate of carboxylation, Vcma x, and maximum rate of electron transport, Jmax), which was estimated by fitting a biochemical photosynthesis model to the CO2-response curves. Nitrogen-use efficiency ( Amax/Na, Na is nitrogen content per leaf area) decreased also with leaf age, whereas Jmax and Vcmax did not correlate with Na. Although measurements were performed during the rainy season, the leaf gas exchange parameter that showed the best correlation with Amax was stomatal conductance ( gs). An asymptotic function was fitted to the Amax- gs relationship, with R2 = 0.85. Amax, Vcmax, Jmax and gs varied more among different whorls in the same clone than among different clones in the same whorl. We concluded that leaf whorl was an appropriate parameter to characterize leaves for the purpose of modelling canopy photosynthesis in field-grown rubber trees, and that stomatal conductance was the most important variable explaining changes in Amax with leaf age in rubber trees. [ABSTRACT FROM AUTHOR]

Rubber trees (Hevea brasiliensis) are the main source of natural rubber, extracted from latex, which exudes from the trunk after tapping. Tapped trees require large amounts of carbon (C) to regenerate the latex after its collection. Knowing the contribution of C sources involved in latex biosynthesis will help in understanding how rubber trees face this additional C demand. Whole crown 13CO2 pulse labelling was performed on 4-year-old rubber trees in June, when latex production was low, and in October, when it was high. 13C content was quantified in the foliage, phloem sap, wood, and latex. In both labelling periods, 13C was recovered in latex just after labelling, indicating that part of the carbohydrate was directly allocated to latex. However, significant amounts of 13C were still recovered in latex after 100 d and the peak was reached significantly later than in phloem sap, demonstrating the contribution of a reserve pool as a source of latex C. The contribution of new photosynthates to latex regeneration was faster and higher when latex metabolism was well established, in October, than in June. An improved understanding of C dynamics and the source-sink relationship in rubber tree is crucial to adapt tapping system practices and ensure sustainable latex production., (© The Author(s) 2020. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)