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The land use change from tropical forests to rubber plantations has had a great influence on ecosystem‐level carbon (C) exchange and soil C dynamics. This study aimed to assess the variation of soil respiration and its components in rubber plantations of different stand age. A trenching method was used to partition soil respiration (RS) into autotrophic respiration (RA) and heterotrophic respiration (RH) for 3 years in 12, 24, 32 and 49‐year‐old rubber plantations. Our results showed that RS changed significantly among rubber plantations, with the highest RS in the old‐growth rubber plantation (49‐year plantation, 147.30 ± 6.91 mg CO2‐C m−2 hr−1) followed by the mature (137.16 ± 7.68 and 108.10 ± 4.83 in 24‐year and 32‐year plantations, respectively) and the young (12‐year plantation, 78.43 ± 3.84 mg CO2‐C m−2 hr−1) rubber plantations. RS was significantly and exponentially related to soil temperature (p < .0001) rather than soil water content, which led to higher RS in the rainy season than in the dry season. The contribution of RA to RS was higher in the mature rubber plantation than in the young (27%) and the old‐growth (20%) rubber plantations. The sensitivity of RS to increasing temperature (Q10) was higher in 32‐ and 49‐year plantations than in 12‐ and 24‐year rubber plantations. The largest Q10 value of RH and RA was found in the old‐growth (49‐year plantation, 2.95) and the mature (32‐year plantation, 8.01) rubber plantations, respectively. Our results highlight the importance of environmental factors in determining the variation in RS in rubber plantations with different stand age. However, further studies are still required to elucidate the mechanisms impacting stand age‐related effects on soil respiration, such as the differences in photosynthesis in rubber plantations. Highlights: Soil respiration (RS) in four rubber plantations of different stand age was examined.RS tended to increase with the increasing stand age.The contribution of autotrophic respiration (RA) to RS was higher in the mature stands.Q10 values of heterotrophic respiration (RH) and RA were higher in old‐growth and mature stands, respectively. [ABSTRACT FROM AUTHOR]

Sulfur spraying is a conventional prevention and control measure for rubber leaf diseases in the northern margin of tropical Southeast Asia. The aim of this study was to determine the long-term (48 years) accumulated effects of sulfur spraying on some major soil microbial and nutrient properties in the area of rubber plantation. The results indicate a significant decrease in pH along the rubber chronosequence with yearly sulfur application. A negative effect of sulfur spraying on soil total sulfur content was also observed. Apart from that, soil microbial characteristics increased significantly, except for microbial biomass carbon. Soil nutrient bioavailability-related characteristics showed a complex pattern of response to sulfur spraying, among which bio-available ammonium nitrogen increased linearly, bio-available nitrate nitrogen showed a trend resembling a large resting capital letter 'S', bio-available phosphorus showed a contrary trend to nitrogen, a capital letter 'S' resting the other direction, whereas bio-available potassium had no response to sulfur spraying. Based on the comprehensive response indexes, soil microbial characteristics had a pulsing response to sulfur spraying accumulation and two critical turning points were sometime between the 23rd and 32nd year and between the 40th and 48th year. Soil nutrient bioavailability showed a volatile comprehensive pattern, but there was no significant difference during the chronosequence. There is need for control sulfur deposition frequency and dosage under the soil and environmental safety threshold in the diseases prevention and control in monoculture rubber plantation. [ABSTRACT FROM AUTHOR]

The pattern of intense defoliation of rubber trees ( Hevea brasiliensis ) in Southwest China is assumed to mainly be attributable to drought stress. However, this has never been proven, and the pattern remains unclear. Our objectives were to reveal the driving factor and pattern of intense defoliation, and to explore the characteristics of sap flow density ( J s ) and relate them to climatic factors before, during and after the intense defoliation period. We continuously measured J s and related climatic factors in a rubber plantation in Southwest China from 2013 to 2016 and found that (1) the cold stress (<10 °C) was more relevant to intense defoliation than drought stress, and after encountering cold stress the rubber trees might enter dormancy for approximately 50 days during the defoliation period; (2) J s showed a self-regulating ability to respond to high air temperature ( T a ) and water vapor pressure deficit ( VPD ) with a time lag of approximately one hour during all periods except during the defoliation period; (3) the sensitivity of J s to T a weaken ( slope  = 0.14, r  = 0.17, P  > 0.05) during the defoliation period, but it rebounded back to a relative high level ( slope  = 1.44, r  = 0.55, P  < 0.01) during the refoliation period which was similar to that during the remaining periods; and (4) the relationship between J s and T a was generally positive, while both SWC 5 and SWC 100 exerted inhibitory effects on J s , and the interactive effects among T a , SWC 5 and SWC 100 on J s were significant during the refoliation period ( P  < 0.01). Based on these findings, we evaluated J s as a crucial physiological indicator of the processes underlying important phenological transition periods, and the cold stress rather than drought stress was likely the driving factor of the pattern of intense defoliation occurred in Southwest China rubber plantations. [ABSTRACT FROM AUTHOR]

• The effect of fog on rubber trees (Hevea brasiliensis) was quantified for 3 years. • Visibility, sap flux density and crop water productivity (WP c) were studied. • Under the fog days, rubber trees were physiologically less active. • Carbon assimilation and evapotranspiration were suppressed but WP c enhanced by fog. • Dry seasonal fog can reduce water demand and alleviate drought stress. The rapid conversion of tropical rainforests into monoculture plantations of rubber (Hevea brasiliensis) in Southeast Asia (SEA) necessitates understanding of rubber tree physiology under local climatic conditions. Frequent fog immersion in the montane regions of SEA may affect the water and carbon budgets of the rubber trees and the plantation ecosystems. We studied the effect of fog on various plant physiological parameters in a mature rubber plantation in southwest China over 3 years. During the study period, an average of 141 fog events occurred every year, and the majority occurred during the dry season, when the temperature was relatively low. In addition to the low temperature, fog events were also associated with low vapor pressure deficit, atmospheric water potential, relative humidity and frequent wet-canopy conditions. We divided the dry season into cool dry (November-February) and hot dry (March-April) seasons and classified days into foggy (FG) and non-foggy (non-FG) days. During the FG days of the cool dry season, the physiological activities of the rubber trees were suppressed where carbon assimilation and evapotranspiration showed reductions of 4% and 15%, respectively, compared to the cool dry non-FG days. Importantly, the unequal declines in carbon assimilation and evapotranspiration led to enhanced crop water productivity (WP c) on cool dry FG days but insignificant WP c values were found between FG and non-FG days of the hot dry season. Our results suggest that, by regulating plant physiology, fog events during the cool dry season significantly reduce water demand and alleviate water stress for the trees through improved WP c. [ABSTRACT FROM AUTHOR]

The survival strategy and ecophysiological process of rubber trees (Hevea brasiliensis), in which water-use efficiency (WUE) represents a vital indicator linking the carbon and water cycles, are mediated by phenology and can be severely affected by a low fruit-set rate and cold stress. However, the phenology-related WUE and its temporal variation as well as its responses to site heterogeneity in rubber plantations remain poorly understood. In this study, we used a four-year (2013–2016) continuous dataset of biometric survey, sap flow and phenology of rubber trees to examine the WUE in response to phenological changes and cold stress. The planting density and stand age, factors exhibiting a considerable difference and contributing to site heterogeneity, were explored to reveal their effects on the WUE of rubber plantations in Yunnan Province of Southwest China. Unexpectedly, the response of the WUE to phenological changes was characterized by the peak value (2.73±0.59 g C kg−1 H 2 O) that occurred simultaneously with the fruiting period (P f), and the WUE values during the P f were significantly higher than that of other phenological periods (P <0.01), indicating that the survival strategy adopted by the rubber trees to cope with the low fruit-set rate as well as cold stress during the defoliation period (P d) and adapt to the local climate might be very effective. However, this effectiveness might be reduced to some extent, since the WUE was significantly affected by the planting density (df =2, F -value=11.51) and stand age (df =3, F -value=22.84) indicated by one-way analysis of variance (P <0.01). These findings can provide a deeper understanding for the adaptation strategies to adverse climate and the cultivation and management of rubber plantations. [Display omitted] • The annual life cycle of rubber trees was divided into four phenological periods. • Water-use efficiency (WUE) revealed the survival strategy of rubber trees. • Maximum WUE values occurred simultaneously with the fruiting period (P f). • The planting density and stand age significantly affected the WUE. • Increases in the planting density tended to decrease the WUE of rubber trees. [ABSTRACT FROM AUTHOR]

The annual pattern of the carbon-water coupling of rubber trees (Hevea brasiliensis) has never been explored on the plant and ecosystem scales, and the responses of the carbon-water coupling to cold stress and hail events remain unknown. We continuously measured the sap flow density (J s), diameter at breast height (DBH), and the carbon and water flux of rubber plantations in Southwest China from 2012 to 2016, to compare the water-use efficiency (WUE) of rubber plantations by considering different scales (plant and ecosystem) and methods (eddy covariance and isotope techniques) and to reveal the adaptation strategy of rubber trees to cold stress and hail events from the perspective of WUE. We found the followings: (1) high correlation in the annual WUE pattern were noted on the plant and ecosystem scales (r =0.74, P <0.05), with higher WUE values obtained during the rainy seasons than during the dry seasons; (2) The rubber trees responded to cold stress with the reduction of the strength of the carbon-water coupling, which was characterized by a lower ratio of growth rate of DBH (R dbh) to J s during the cold stress period (slope =0.007, P >0.05) compared with after the cold stress (slope =0.03, P <0.05); and (3) The hail event severely disrupted the WUE pattern of rubber trees, which was characterized by a weak relationship between R dbh and J s after experiencing the hail event (slope =0.01, r =0.35, P >0.05) than without experiencing the hail event (slope =0.07, r =0.63, P <0.05). We concluded that the response of rubber trees to the frequent cold stress might involve the long-term adaptation by short-term decoupling of WUE ; however, the effects of the occasional hail event on the growth of rubber trees were more profound. [Display omitted] • Water-use efficiency (WUE) revealed the adaption of rubber trees to cold stress. • The WUE of rubber trees was highly correlated on plant and ecosystem scales. • Rubber trees adapted to cold stress by decoupling the WUE for a short period. • Hail event severely reduced the WUE of rubber trees on the plant scale. • Hail event had greater effects on photosynthesis than transpiration of rubber trees. [ABSTRACT FROM AUTHOR]

• Comparing tropical rainforest (TRF) to rubber plantation (RP) emissions, CH 4 sink decreased and CO 2 emission was similar. • Leaf area index and soil water content mainly influences soil CO 2 and CH 4 emissions in RP respectively. • Soil water content, soil temperature, and dead fine roots were the most important factors of soil CO 2 and CH 4 emissions in TRF. • Soil temperature and fine root growth explained the difference in soil CO 2 and CH 4 between TRF and RP. Soil CO 2 (a) and CH 4 (b) fluxes in tropical rainforest (black circles) and rubber plantation (open circles) at Xishuangbanna, Southwest China. [Display omitted] [ABSTRACT FROM AUTHOR]