The hydraulic conductance of Fraxinus ornus leaves is constrained by soil water availability and coordinated with gas exchange rates

Leguizamón, E. S., Yanniccari, M. E., Guiamet, J. J. and Acciaresi, H. A. 2011. Growth, gas exchange and competitive ability of Sorghum halepense populations under different soil water availability. Can. J. Plant Sci. 91: 1011–1025. Different studies have determined that environmental variation is a key factor determining the outcome of competition within plant communities. Considering the importance of the resource water in non-irrigated lands of Argentina, the aim was to determine the effects of water deficit on relative growth rate (RGR), root length ratio (RLR), gas exchange and competitive ability of Sorghum halepense populations collected in humid and subhumid regions of the Pampa plains. Under semi-controlled conditions, we compared plants of seven S. halepense populations subjected to three different levels of soil water availability during 3 wk: Field capacity (FC), 75% FC and drought (D). Moreover, total above-ground biomass of S. halepense and Zea mays plants growing together in competition was determined. It was found that those plants collected in humid or subhumid regions had greater RGR, gas exchange and RLR under FC and D, respectively. Zea mays achieved a higher competitive ability than S. halepense under FC, but plants collected in humid regions out-competed the crop when grown at 75% FC. Sorghum halepense plants collected in subhumid regions dominated under D. Root length ratio may have favored the maintenance of high levels of gas exchange and also high RGR, thus contributing to sustain a competitive hierarchy under soil water stress.

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Characterizing Growing Season Length of Subtropical Coniferous Forests with a Phenological Model

Forests ◽

10.3390/f12010095 ◽

2021 ◽

Vol 12 (1) ◽

pp. 95

Author(s):

Yuan Gong ◽

Christina L. Staudhammer ◽

Susanne Wiesner ◽

Gregory Starr ◽

Yinlong Zhang

Keyword(s):

Climate Change ◽

Soil Water ◽

Prescribed Fire ◽

Water Availability ◽

Longleaf Pine ◽

Growing Season ◽

Soil Water Availability ◽

Future Climate Change ◽

Short Term ◽

Phenological Model

Understanding plant phenological change is of great concern in the context of global climate change. Phenological models can aid in understanding and predicting growing season changes and can be parameterized with gross primary production (GPP) estimated using the eddy covariance (EC) technique. This study used nine years of EC-derived GPP data from three mature subtropical longleaf pine forests in the southeastern United States with differing soil water holding capacity in combination with site-specific micrometeorological data to parameterize a photosynthesis-based phenological model. We evaluated how weather conditions and prescribed fire led to variation in the ecosystem phenological processes. The results suggest that soil water availability had an effect on phenology, and greater soil water availability was associated with a longer growing season (LOS). We also observed that prescribed fire, a common forest management activity in the region, had a limited impact on phenological processes. Dormant season fire had no significant effect on phenological processes by site, but we observed differences in the start of the growing season (SOS) between fire and non-fire years. Fire delayed SOS by 10 d ± 5 d (SE), and this effect was greater with higher soil water availability, extending SOS by 18 d on average. Fire was also associated with increased sensitivity of spring phenology to radiation and air temperature. We found that interannual climate change and periodic weather anomalies (flood, short-term drought, and long-term drought), controlled annual ecosystem phenological processes more than prescribed fire. When water availability increased following short-term summer drought, the growing season was extended. With future climate change, subtropical areas of the Southeastern US are expected to experience more frequent short-term droughts, which could shorten the region’s growing season and lead to a reduction in the longleaf pine ecosystem’s carbon sequestration capacity.

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