Soil Moisture In Plots Research Articles

Thermal tolerance and growth responses to in situ soil water reductions among alpine plants

ABSTRACT Background Changes to precipitation patterns and warming temperatures are predicted to reduce the water available to Australian alpine plants during the growing season. Soil water deficits are likely to co-occur with frost extremes that are common throughout the year and heatwaves which are increasing in severity with ongoing climate change. Aims We aimed to determine whether co-occurring reductions in soil moisture would affect the capacity of alpine plants to tolerate temperature extremes. Methods We used small rainout shelters to impose a drought treatment in situ in the alpine zone, which chronically reduced soil moisture in plots of alpine plant species including evergreen shrubs, graminoids and perennial forbs. We determined photosynthetic freezing tolerance and heat tolerance during the growing season across 2 years, and measured plant growth, in response to the drought treatment. Results Thermal tolerance was insensitive to chronically reduced soil moisture, and graminoids exhibited overall greater freezing and heat tolerance thresholds than other life forms. The drought treatment improved shrub growth, likely due to the amelioration of wind and the slightly warmer temperatures provided by the rainout shelters. Conclusion We conclude that Australian alpine plants maintain high tolerances to both high- and low-temperature extremes during the growing season and are relatively robust to combined temperature extremes and reductions in near-surface soil moisture that are likely to occur with ongoing climate warming.

Effect of Wetting Agent on Nutrient and Water Retention and Runoff from Simulated Urban Lawns

Wetting agents have been widely used in the turf industry for ameliorating hydrophobic soil conditions and improving water use efficiency. However, limited information is available regarding potential benefits of wetting agents on fine textured soil lawns where wettable soils are commonly found, because most prior studies have been conducted in sand-based turf systems. This 2-year field study evaluated the potential for wetting agents to improve turf quality, as well as to reduce runoff losses of water and nutrients from st. augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] lawns. Over two seasons, turfgrass quality, percent green cover, and soil moisture in plots were evaluated in response to wetting agent and fertilizer treatments. During precipitation events, total runoff volumes were measured, as well as total export of nutrients including NO3-N, NH4-N, total dissolved N, dissolved organic N, dissolved organic C, and PO4-P. No runoff was detected from any treatments when precipitation was less than 13 mm. St. augustinegrass turfgrass quality and soil moisture were slightly improved by wetting agent and fertilizer treatments during the study, but no significant effects of either of the treatments were found on runoff volumes or nutrient exports. Although turf was managed under deficit irrigation levels of 0.3 × reference evapotranspiration, irrigation events were not withheld due to rainfall, and thus, little to no drought stress was observed during the study.

Soil physical properties and crop response in direct seeding of spring barley as affected by wheat straw level

The outcome of direct seeding is influenced by sowing technology and residue management, and by water disposal in semiarid conditions. Most studies regarding direct seeding include little information about the amount of residue at sowing time. This paper shows the results of a no-till seeding of barley (Hordeum vulgare L.) with different levels of wheat (Triticum aestivum L.) straw. Experiments were carried out from 2012 to 2015, and treatments consisted of three different wheat straw levels to represent three common scenarios depending on the way farmers manage straw. Bulk density and soil moisture content were measured at three different stages: germination, anthesis, and tillering. Measurements included sowing depth, emergence rate, yield, and harvest index. Soil moisture was related to residue level, with higher soil moisture in plots with higher amounts of straw, reaching a maximum increase of 39% in 2015 at the stage of tillering, when minimum water content was present. Similarly, the lower significant differences in soil water content between residue levels were found when soil had higher water content values. Emergence rate was affected by residue level in all years, and rates had a maximum variation in 2013 when they ranged between 31.7% in the highest level of residues and 81.8% in residue removed plots. Yield was affected by residue level, mainly in years 2013 and 2014 when the lowest production of grain took place, with a minimum of 35% decrease in plots with highest amount of straw. No effect on harvest index was observed in this experiment. A higher amount of residues positively affected soil water content, but it decreased plant emergence rate. Consequently, yield was negatively affected by the level of residue cover. Therefore, removing excessive crop residues in spring barley can be a good practice in rainfed conditions and warm Mediterranean climates.

Changes in plant community composition and reduced precipitation have limited effects on the structure of soil bacterial and fungal communities present in a semiarid grassland

To assess the impacts of precipitation and plants on soil bacterial and fungal communities, precipitation was reduced and plants were removed from experimental plots in a semiarid grassland. For plots with reduced precipitation, rainout shelters were constructed using clear, corrugated polycarbonate panels. Plant removal plots had plants extracted manually to remove both above- and belowground portions, and these plots were kept free of vegetation for the duration of the experiment. High-throughput sequencing of the 16S rRNA gene and fungal ITS region was used to assess the response of soil microbial communities to experimental manipulations. Soil moisture content, inorganic nitrogen concentrations, and aboveground plant biomass were also examined in these experimental plots. Soil moisture in plots with reduced precipitation was on average 40 % lower than that in control plots, while soil moisture in plant removal plots resembled that of control plots. No significant differences in available nitrogen were observed among treatments. Plots with reduced precipitation contained significantly less aboveground biomass than control plots, and also displayed a significantly higher occurrence of Russian thistle, an annual exotic. Soil bacterial and fungal communities were impacted by reduced precipitation, plant removal, and time, though these differences were subtle. Climate-change associated reductions in precipitation and vegetation will not cause large shifts in soil microbial communities on short time scales.

Determination of Moisture Deficit and Heat Stress Tolerance in Corn Using Physiological Measurements and a Low‐Cost Microcontroller‐Based Monitoring System

AbstractIn the southern United States, corn production encounters moisture deficit coupled with high‐temperature stress, particularly during the reproductive stage of the plant. In evaluating plants for environmental stress tolerance, it is important to monitor changes in their physical environment under natural conditions, especially when there are multiple stress factors, and integrate this information with their physiological responses. A low‐cost microcontroller‐based monitoring system was developed to automate measurement of canopy, soil and air temperatures, and soil moisture status in field plots. The purpose of this study was to examine how this system, in combination with physiological measurements, could assist in detecting differences among corn genotypes in response to moisture deficit and heat stress. Three commercial hybrids and two inbred germplasm lines were grown in the field under irrigated and non‐irrigated conditions. Leaf water potential, photosynthetic pigments, cell membrane thermostability (CMT) and maximum quantum efficiency of photosystem II (Fv/Fm) were determined on these genotypes under field and greenhouse conditions. Variations observed in air and soil temperatures, and soil moisture in plots of the individual corn genotypes helped explain their differences in canopy temperature (CT), and these variations were reflected in the physiological responses. One of the commercial hybrids, having the lowest CT and the highest CMT, was the most tolerant among the genotypes under moisture deficit and heat stress conditions. These results demonstrated that the low‐cost microcontroller‐based monitoring system, in combination with physiological measurements, was effective in evaluating corn genotypes for drought and heat stress tolerance.

Plot‐ and watershed‐scale soil moisture variability in a humid Piedmont watershed

We investigate space‐time dynamics of soil water through extreme drought and wet periods for a Mid‐Atlantic Piedmont catchment. Soil moisture is a nonlinear control of soil nitrogen cycling processes, providing “hot spot” and “hot moment” dynamics that are not well modeled using time‐ or space‐averaged conditions. We document spatial variation in near‐surface soil moisture and examine relationships between mean and variance in soil moisture at plot and watershed scales. Riparian plot soil moisture spatial variance was significantly higher than the variance in uplands and was high relative to soil moisture variance reported by other studies. Plot soil moisture means closely followed a linear trend with the topographic wetness index. However, high within‐plot variance obscured this relationship for experiments where smaller subsets of samples were used, emphasizing the importance of replicate plot measurements to account for fine‐scale heterogeneity in soil moisture. We demonstrate the importance of these spatial‐temporal patterns of soil moisture for estimates of hydrologic controls on biogeochemical cycling by showing that undersampling of fine‐scale soil moisture variation is likely to lead to overestimation and underestimation of nitrification and denitrification, respectively.

Roots, soil water and crop yield: tree-crop interactions in a semi-arid agroforestry system in Kenya

Variations in soil water, crop yield and fine roots of 3–4 year-old Grevillea robusta Cunn. and Gliricidia sepium (Jacq.) Walp. growing in association with maize (Zea mays L.) were examined in semiarid Kenya during the long rains of 1996 and 1997. Even although tree roots penetrated more deeply than maize roots, maximum root length densities for both tree species and maize occurred in the top 200 mm of the soil profile where soil moisture was frequently recharged by rains. Populations of roots in plots containing trees were dominated by tree roots at the beginning of the growing season but because tree roots died and maize root length increased during the cropping season, amounts of tree and maize roots were similar at the end of the season. Thus, there was evidence of temporal separation of root activity between species, but there was no spatial separation of the rooting zones of the trees and crops within that part of the soil profile occupied by crop roots. Tree root length density declined with increasing distances from rows of trees and with depth in the soil profile. Although Grevillea trees were largest, plots containing G. sepium trees always contained more tree roots than plots containing G. robusta trees and Gliricidia was more competitive with maize than Grevillea. Overall, Gliricidia reduced crop yield by about 50% and Grevillea by about 40% relative to crop yield in control plots lacking trees and reductions of crop yield were greatest close to trees. There was less soil moisture in plots containing trees than in control plots. Such difference between control plots and plots containing trees were maximal at the end of the dry season and there was always less soil moisture close to trees than elsewhere in the plots. Plots containing Gliricidia trees contained less soil water than plots containing Grevillea trees.

Overlaying compacted or uncompacted construction fill has no negative impact on white oak and sweetgum growth and physiology

Raising the soil grade, frequently required during building construction, is thought to damage trees and is of concern to foresters responsible for tree protection on such sites. We investigated the effects of applying fill over the roots of 22-year-old white oaks (Quercus alba L.) and 13-year-old sweetgums (Liquidambar styraciflua L.). Treatments included a control (no fill), fill (sandy loam C horizon soil spread 20 cm deep), and compacted fill (same as fill but compacted). Trees with fill had soil held away from trunks or not. After 3 years, there was no consistent treatment effect on growth, chlorophyll fluorescence, or soil respiration in either species. Fill disrupted normal soil moisture patterns. White oak plots with fills had lower soil water contents than controls. In sweetgum plots, soil underlying fill was typically drier than fill layers, whereas control plot soil moisture tended to increase with depth. Fills did not affect overall root density for either species. White oak grew roots well into fill soils, but sweetgum did not, although sweetgum root distribution shifted upwards under fills. Other factors associated with raising the grade, such as soil trafficking and root severance, may be responsible for much of the tree decline attributed to fill.

The seed bank in an old-growth, temperate deciduous forest

We assessed the size and composition of the seed bank in 31 plots representing a range of habitats within an old-growth, temperate deciduous forest at Mont St. Hilaire, Québec, Canada. We identified 49 taxa in the seed bank, with an average of 40 species·m-2 and a median density of 1218 seeds·m-2. The most frequent seeds were species of Carex and Rubus, Diervilla lonicera, and Eupatorium rugosum, while seeds of Carex were the most numerous overall. Of the 12 species in the seed bank not found in the forest, 11 were found growing on the developed landscape surrounding this 10-km2 forest fragment. These nonforest species were numerically only a minor component of the forest seed bank. Vernal herbs were not in the seed bank, and there were only a few tree species. Variation in seed bank richness among habitats was correlated positively with canopy cover, soil moisture, and soil nutrients, but not with the seed bank density or total number of species in the aboveground vegetation. Seed bank density increased with plot soil moisture. Woody species predominated in the seed bank of plots with richer soils, deeper litter, and more closed canopies. Herbaceous species predominated in the seed bank of plots with more open canopies, more mesic water regimes, and greater species richness in the aboveground vegetation. Contrary to earlier results suggesting forest seed banks primarily include shade-intolerant species associated with canopy disturbance or secondary succession, the seed bank in this old-growth, primary forest contains many shade-tolerant forest species.Key words: seed bank, old-growth forest, primary forest, temperate deciduous forest, habitat diversity, seed dispersal.

The seed bank in an old-growth, temperate deciduous forest

We assessed the size and composition of the seed bank in 31 plots representing a range of habitats within an old-growth, temperate deciduous forest at Mont St. Hilaire, Quebec, Canada. We identified 49 taxa in the seed bank, with an average of 40 species·m -2 and a median density of 1218 seeds·m -2 . The most frequent seeds were species of Carex and Rubus, Diervilla lonicera, and Eupatorium rugosum, while seeds of Carex were the most numerous overall. Of the 12 species in the seed bank not found in the forest, 11 were found growing on the developed landscape sur- rounding this 10-km 2 forest fragment. These nonforest species were numerically only a minor component of the forest seed bank. Vernal herbs were not in the seed bank, and there were only a few tree species. Variation in seed bank rich- ness among habitats was correlated positively with canopy cover, soil moisture, and soil nutrients, but not with the seed bank density or total number of species in the aboveground vegetation. Seed bank density increased with plot soil moisture. Woody species predominated in the seed bank of plots with richer soils, deeper litter, and more closed cano- pies. Herbaceous species predominated in the seed bank of plots with more open canopies, more mesic water regimes, and greater species richness in the aboveground vegetation. Contrary to earlier results suggesting forest seed banks pri - marily include shade-intolerant species associated with canopy disturbance or secondary succession, the seed bank in this old-growth, primary forest contains many shade-tolerant forest species.