Modelling the effects of soil water limitations on transpiration and stomatal regulation of cauliflower

Trials were undertaken at two sites with contrasting soil types in the Wimmera region of Victoria: a well-structured grey cracking clay soil (Vertosol) at Traynors Lagoon and a poorly structured sodic clay soil (Sodosol) at Gre Gre. The effect of a once-off application of three different types of bedding litter (wheat straw and two types of rice hulls) applied at three rates (20, 30 and 40 t/ha) was compared with that of a control (no amelioration), nitrogen fertiliser (46 kg N/ha) applied to each crop, or nitrogen plus a once-off application of gypsum (2.5 t/ha). The growth of three subsequent crops and soil water was examined. Pig bedding litter (rice hulls 1, rice hulls 2 or wheat straw) produced marked improvements in the dry matter production and grain yield of the first crop (wheat) in 1997 and a following canola crop in 1998. In 1999, bedding litter significantly improved the growth of an oats crop at Gre Gre, but had no effect on a crop of field peas at Traynors Lagoon. The beneficial effects of bedding litter on grain yields, however, were matched by small but significant reductions in grain quality resulting from soil water limitations for the yield potential. Although crop growth was improved by the addition of nitrogen fertiliser each year or both nitrogen plus gypsum, the effect was usually small compared with that of adding litter and provided minimal residual value in the following year. There was a general trend for gravimetric soil water to be higher at sowing where bedding litter had been applied, especially at Gre Gre. In contrast, soil water tended to be lower at grain maturity at Traynors Lagoon, where bedding litter or nitrogen fertiliser had been applied, reflecting the enhanced crop growth in these treatments compared with the control. There was no consistent effect of treatments on soil water at maturity in either 1998 or 1999 at Gre Gre.

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Large and projected strengthening moisture limitation on end-of-season photosynthesis

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1914436117 ◽

2020 ◽

Vol 117 (17) ◽

pp. 9216-9222 ◽

Cited By ~ 7

Author(s):

Yao Zhang ◽

Nicholas C. Parazoo ◽

A. Park Williams ◽

Sha Zhou ◽

Pierre Gentine

Keyword(s):

Soil Water ◽

Growing Season ◽

Energy Availability ◽

Wet Season ◽

Late Season ◽

Vegetation Activity ◽

Future Warming ◽

Water Limitations ◽

Using Data ◽

Underlying Mechanisms

Terrestrial photosynthesis is regulated by plant phenology and environmental conditions, both of which experienced substantial changes in recent decades. Unlike early-season photosynthesis, which is mostly driven by temperature or wet-season onset, late-season photosynthesis can be limited by several factors and the underlying mechanisms are less understood. Here, we analyze the temperature and water limitations on the ending date of photosynthesis (EOP), using data from both remote-sensing and flux tower-based measurements. We find a contrasting spatial pattern of temperature and water limitations on EOP. The threshold separating these is determined by the balance between energy availability and soil water supply. This coordinated temperature and moisture regulation can be explained by “law of minimum,” i.e., as temperature limitation diminishes, higher soil water is needed to support increased vegetation activity, especially during the late growing season. Models project future warming and drying, especially during late season, both of which should further expand the water-limited regions, causing large variations and potential decreases in photosynthesis.

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Effects of groundwater abstraction on two keystone tree species in an arid savanna national park

PeerJ ◽

10.7717/peerj.2923 ◽

2017 ◽

Vol 5 ◽

pp. e2923 ◽

Cited By ~ 7

Author(s):

Eleanor Shadwell ◽

Edmund February

Keyword(s):

Soil Water ◽

Water Use ◽

Water Table ◽

Tree Species ◽

Dry Season ◽

Leaf Water ◽

Groundwater Abstraction ◽

Stomatal Regulation ◽

Water Potentials ◽

Large Trees

BackgroundIn arid systems with no surface water, deep boreholes in ephemeral river beds provide for humans and animals. With continually increasing infrastructure development for tourism in arid wildlife parks such as the Kgalagadi Transfrontier Park in southern Africa, we ask what effects increased abstraction may have on large trees. Large trees in arid savannas perform essential ecosystem services by providing food, shade, nesting sites and increased nutrients for many other plant and animal species and for this are regarded as keystone species.MethodsWe determine seasonal fluctuations in the water table while also determining the water source for the dominant large tree species in the Auob and Nossob rivers in the Park. We also determine the extent to which these trees are physiologically stressed using leafδ13C, xylem pressure potentials, specific leaf area and an estimate of canopy death. We do this both upstream and downstream of a low water use borehole in the Auob River and a high water use borehole in the Nossob River.ResultsOur results show that the trees are indeed using deep groundwater in the wet season and that this is the same water used by people. In the dry season, trees in the Auob downstream of the active borehole become detached from the aquifer and use more isotopically enriched soil water. In the Nossob in the dry season, all trees use isotopically enriched soil water, and downstream of the active borehole use stomatal regulation to maintain leaf water potentials. These results suggest that trees in the more heavily utilised Nossob are under more water stress than those trees in the Auob but that trees in both rivers demonstrate physiological adaptation to the changes in available water with smaller heavier leaves, no significant canopy dieback and in the dry season in the Nossob stomatal regulation of leaf water potentials.DiscussionAn increase in abstraction of groundwater particularly at the Nossob borehole may cause an additional draw down of the water table adding to the physiological stress demonstrated in our study. The managers of the Kgalagadi Transfrontier Park have a mandate that includes biodiversity conservation. To fulfil this mandate, upper and lower thresholds for groundwater abstraction that allow for an adequate ecological reserve have to be determined.

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