Much of humanity relies on rice (Oryza sativa) as a food source, but cultivation is water intensive and the crop is vulnerable to drought and high temperatures. Under climate change, periods of ...reduced water availability and high temperature are expected to become more frequent, leading to detrimental effects on rice yields.
We engineered the high-yielding rice cultivar ‘IR64’ to produce fewer stomata by manipulating the level of a developmental signal. We overexpressed the rice epidermal patterning factor OsEPF1, creating plants with substantially reduced stomatal density and correspondingly low stomatal conductance.
Low stomatal density rice lines were more able to conserve water, using c. 60% of the normal amount between weeks 4 and 5 post germination. When grown at elevated atmospheric CO2, rice plants with low stomatal density were able to maintain their stomatal conductance and survive drought and high temperature (40°C) for longer than control plants. Low stomatal density rice gave equivalent or even improved yields, despite a reduced rate of photosynthesis in some conditions.
Rice plants with fewer stomata are drought tolerant and more conservative in their water use, and they should perform better in the future when climate change is expected to threaten food security.
Patterns, mechanisms, projections, and consequences of tree mortality and associated broad-scale forest die-off due to drought accompanied by warmer temperatures-"hotter drought", an emerging ...characteristic of the Anthropocene-are the focus of rapidly expanding literature. Despite recent observational, experimental, and modeling studies suggesting increased vulnerability of trees to hotter drought and associated pests and pathogens, substantial debate remains among research, management and policy-making communities regarding future tree mortality risks. We summarize key mortality-relevant findings, differentiating between those implying lesser versus greater levels of vulnerability. Evidence suggesting lesser vulnerability includes forest benefits of elevated CO
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and increased water-use efficiency; observed and modeled increases in forest growth and canopy greening; widespread increases in woody-plant biomass, density, and extent; compensatory physiological, morphological, and genetic mechanisms; dampening ecological feedbacks; and potential mitigation by forest management. In contrast, recent studies document more rapid mortality under hotter drought due to negative tree physiological responses and accelerated biotic attacks. Additional evidence suggesting greater vulnerability includes rising background mortality rates; projected increases in drought frequency, intensity, and duration; limitations of vegetation models such as inadequately represented mortality processes; warming feedbacks from die-off; and wildfire synergies. Grouping these findings we identify ten contrasting perspectives that shape the vulnerability debate but have not been discussed collectively. We also present a set of global vulnerability drivers that are known with high confidence: (1) droughts eventually occur everywhere; (2) warming produces hotter droughts; (3) atmospheric moisture demand increases nonlinearly with temperature during drought; (4) mortality can occur faster in hotter drought, consistent with fundamental physiology; (5) shorter droughts occur more frequently than longer droughts and can become lethal under warming, increasing the frequency of lethal drought nonlinearly; and (6) mortality happens rapidly relative to growth intervals needed for forest recovery. These high-confidence drivers, in concert with research supporting greater vulnerability perspectives, support an overall viewpoint of greater forest vulnerability globally. We surmise that mortality vulnerability is being discounted in part due to difficulties in predicting threshold responses to extreme climate events. Given the profound ecological and societal implications of underestimating global vulnerability to hotter drought, we highlight urgent challenges for research, management, and policy-making communities.
Individual mangrove tree parameters are necessary for the efficient management and protection of this unique ecosystem, but to measure them using remote sensing (RS) is still a new and challenging ...task due to the high clumping density of mangrove crowns and the relatively low spatial resolution of RS data. Unmanned aerial vehicles (UAVs), as an emerging RS technique, significantly improves the spatial resolution, but has not been used for individual mangrove analysis. This study presents the first investigation into the possibility of individual tree detection and delineation (ITDD) for mangroves using light detection and ranging (LiDAR) data (91 pt./m2) collected from UAV. Specifically, we aim to detect and measure tree height (TH) and crown diameter (CD) of each mangrove tree, and analyze the impact of crown clumping density and spatial resolution on mangrove ITDD. To this end, we combined the variable window filtering method and marker controlled watershed segmentation algorithm, and successfully delineated 46.0% of the 126 field measured mangroves. This was promising considering the complexity of mangrove forest. TH and CD were estimated with higher accuracies than previous studies. The isolated trees, with the lowest clumping density, were delineated with the highest accuracy. To identify the optimal spatial resolution of canopy height model (CHM), we defined four spatial resolutions (0.1 m, 0.25 m, 0.5 m, and 1 m) and conducted a simulation. Based on the results, we propose a rule-of-thumb that the spatial resolution should be finer than one-fourth of CD for ITDD, which is also applicable to other forest types. The main difficulty for mangrove ITDD is an overall under-detection of trees, which is caused by the high clumping density and limited height difference between adjacent mangroves. We recommend combining UAV LiDAR with imagery and terrestrial LiDAR to improve the mangrove ITDD performance.
•First work to delineate individual mangrove crowns using UAV LiDAR data.•Individual mangrove tree height and crown diameter are accurately estimated.•For crown delineation, spatial resolution should be finer than 1/4 crown diameter.
Because environmentally degrading inorganic fertilizer use underlies current worldwide cereal yields, future agricultural sustainability demands enhanced nitrogen use efficiency. We found that ...genome-wide promotion of histone H3 lysine 27 trimethylation (H3K27me3) enables nitrogen-induced stimulation of rice tillering: APETALA2-domain transcription factor NGR5 (NITROGEN-MEDIATED TILLER GROWTH RESPONSE 5) facilitates nitrogen-dependent recruitment of polycomb repressive complex 2 to repress branching-inhibitory genes via H3K27me3 modification. NGR5 is a target of gibberellin receptor GIBBERELLIN INSENSITIVE DWARF1 (GID1)-promoted proteasomal destruction. DELLA proteins (characterized by the presence of a conserved aspartate-glutamate-leucine-leucine-alanine motif) competitively inhibit the GID1-NGR5 interaction and explain increased tillering of green revolution varieties. Increased NGR5 activity consequently uncouples tillering from nitrogen regulation, boosting rice yield at low nitrogen fertilization levels. NGR5 thus enables enhanced nitrogen use efficiency for improved future agricultural sustainability and food security.
'Speed breeding' (SB) shortens the breeding cycle and accelerates crop research through rapid generation advancement. SB can be carried out in numerous ways, one of which involves extending the ...duration of plants' daily exposure to light, combined with early seed harvest, to cycle quickly from seed to seed, thereby reducing the generation times for some long-day (LD) or day-neutral crops. In this protocol, we present glasshouse and growth chamber-based SB approaches with supporting data from experimentation with several crops. We describe the conditions that promote the rapid growth of bread wheat, durum wheat, barley, oat, various Brassica species, chickpea, pea, grass pea, quinoa and Brachypodium distachyon. Points of flexibility within the protocols are highlighted, including how plant density can be increased to efficiently scale up plant numbers for single-seed descent (SSD). In addition, instructions are provided on how to perform SB on a small scale in a benchtop growth cabinet, enabling optimization of parameters at a low cost.
•Higher planting densities resulted in more water use.•Both spacing and genotype directly affected water balance components.•Densities higher than about 1000 tree ha−1 are not recommended for very ...high potential productivity sites.•Lower planting densities can reduce water stress and balance wood production and water conservation.
High stocking short rotation plantations provide high yields for bioenergy use and have been adopted worldwide, especially in tropical areas. This silvicultural approach might alter ecosystem water balances compared with lower stocking, longer rotation practices. The sensitivity of water balance to stocking might also differ among genotypes. We evaluated the primary components of ecosystem water balance (transpiration - Et, canopy interception - Ei, soil evaporation – Es) for two hybrid clones that differ in drought tolerance and productivity (E. urophylla × E. grandis, Clone B2 and E.grandis × E.camaldulensis, Clone C3) planted in stockings ranging from 590 to 2,950 tree ha.-1 in a tropical region in Brazil. On a monthly time step, all water balance components of the two clones were largely related to the seasonality of rainfall, where the wet season represented 73% of the total rainfall, these processes corresponded on average to 76, 75, 67 and 70% of annual canopy interception, soil evaporation, transpiration and evapotranspiration (ET), respectively. For both clones, temperature (R2 = 0.32) and precipitation (R2 > 0.76) explained evapotranspiration responses while adding stocking as a second independent variable slightly improving the model for clone B2 but no improvement was detected for clone C3. When scaling up the monthly data to yearly analyses, all water balance components responded strongly to tree stocking for both clones during the two years of measurements (1.7 to 3.7 years-old). Annual transpiration rose linearly with stocking for the clone B2, rising from 550 mm yr−1 up to 1,039 mm yr−1, corresponding to 53–100% of precipitation (P). The clone C3 showed a much weaker influence of stocking on transpiration, rising only from 550 mm yr−1 at low stocking to 650 mm yr−1 at high stocking (53–63% of P). Canopy interception rose from about 230 mm yr−1 at low stocking to 300 mm yr−1 at high stocking, with little difference between the clones, ranging from 21 to 30% of P. Evaporation from the soil decreased with increased stocking for both clones and represented an average of 20–12% of P from lowest to highest stocking. Total evapotranspiration (ET – sum of Et, Ei and Es) was about 1,000 to 1,050 mm yr−1 at low-to-moderate stockings of both clones, but the less-drought tolerant clone B2 showed substantially higher total evapotranspiration at high stocking (2,900 mm yr−1) compared to the clone C3 (2300 mm yr−1). The difference between precipitation and evapotranspiration (the overall ecosystem water balance) declined with increasing stocking, dropping below 0 at stockings higher than 1,030 tree ha−1 for both clones. High stocking in highly productive Eucalyptus plantations may be less sustainable across multiple rotations, since any deficit in the ecosystem water balance would need to come from longer-term soil water storage. Our results indicate that both genetics and tree stocking can be used as silviculture tools to manage the sustainably of short rotation forest plantations in the face of climate change.
•We studied 16 sites, 18 clones and stocking 480 to 3300 trees ha−1.•High stocking doubled growth on sites with no water deficit; no effect on driest sites.•Stocking response was higher for more ...productive genotypes.•Maximum stocking for > 80% survival ranged from 2900 to 900 trees ha−1.•Optimal stocking tests are most important for high-productivity clones and sites.
Stocking in forests strongly influence stand growth by influencing resource capture, tree survival, and competition between trees and understory vegetation. Many studies have examined these patterns for specific locations and conditions, though with limited populations of inference. The influence of stocking was examined in the TECHS experimental platform, at 16 sites, with 18 clones, across a 2100 km geographic gradient. Stocking was examined by varying spacing within columns, with constant (3-m) spacing between rows. We examined how wood production and quality related to genotypes and environmental conditions, with stocking ranging from 480 to 3300 trees ha−1. Mean annual increment (Mg ha−1 yr−1) for the entire rotation increased with stocking, asymptoting above 1500 trees ha−1. Water-stressed sites had much lower responses to stocking levels than wetter sites. The three driest sites showed only a 25% increase in MAI (7 to 9 Mg ha−1 yr−1) with stocking increases from 480 to 3300 trees ha−1, whereas the 3 most productive sites increased by 50% (20 Mg ha−1 yr−1 to 30 Mg ha−1 yr−1). A similar result occurred for the clones, where the response to the change in stocking was higher in the more productive clones. From a qualitative point of view, tree breakage declined as stocking increased, going from 0% of broken trees in the highest stocking to a maximum of 3% with the stocking of around 480 trees ha−1. Injury to trees increased with stocking, going from about 4 to 9%. Mortality showed a similar pattern, increasing from 8 to 14% with increasing stocking. The percentage of intact (surviving, undamaged) trees at the lowest stocking was 83%, reaching a peak of 94% between 700 and 1100 trees ha−1, declining again to about 85% at the densest stocking. Survival rates declined when stocking exceeded 2900 trees ha−1 on wetter sites, compared with just 900 trees ha−1 on the driest sites. Overall, an increase in stocking from 480 trees ha−1 to 3300 trees ha−1 led to 50% increase in growth. To put this in perspective, the poorest 25% of sites averaged 59% less growth than the top 25%. The poorest 25% of genotypes grew 47% less than the best 25%. The interactions of effects, such as stocking by site, had effects that were of the same magnitude as these main effects. Management decisions about optimal stocking may be substantially improved by considering the main effects and especially their interactions.
•Only stand density kept below 297 TPH from age 7 reduced MOE, MOR, and specific gravity.•As planting density declined the age of transition corewood to outerwood decreased.•Specific gravity was ...similar among planting densities at a well-drained site.•Outerwood transition occurred earlier for a relocated Coastal Plain genotype.•A relocated Coastal Plain genotype had higher latewood proportion.
Changes in ownership and forest product use patterns have incentivized growing loblolly pine (Pinus taeda L.) for chip-and-saw and sawtimber in shorter rotations in the southeastern United States. These management objectives can be accomplished by relatively low stand densities and moving fast-growing genotypes from the Atlantic Coastal Plain to other regions of the loblolly pine range, but wood quality concerns accompany these silvicultural options. In three trials in the Western Gulf region of the mid-South United States, effects of stand density management options on key wood properties (specific gravity, corewood (juvenile wood) diameter, corewood proportion, latewood proportion, corewood:outerwood (juvenile wood:mature wood) transition age as determined using specific gravity) were tested. At one site, clearwood modulus of elasticity (MOE) and modulus of rupture (MOR) were measured. Genotypes of Atlantic Coastal Plain and Western Gulf origin were also tested at two sites. In a trial in which stand density was managed at diverse levels through sequential thinning, beginning at precommercial size, only a regime that was commercially thinned to half its density two times from 297 TPH at age 7 to 62 TPH by age 41 had significant reductions in MOE, MOR, and specific gravity. Corewood diameter increased with decreasing planting density at two sites at the northwestern edge of the loblolly pine range, but corewood proportion declined with decreasing planting density due to greater diameter growth and earlier transition from corewood to outerwood. Specific gravity differences among planting densities was site-specific, with no differences at the more well-drained site. Latewood proportion, which was greater at higher planting densities, was more strongly correlated with specific gravity differences among planting densities. A planting density between 1075 and 1680 TPH would likely be optimum for these site conditions for balancing tree volume growth with minimizing reductions in specific gravity associated with reduced latewood proportion and larger corewood size. The Atlantic Coastal Plain genotype retained its tendencies to transition to outerwood earlier and have greater latewood proportions relative to a local genotype when planted at these Western Gulf sites, and its specific gravity was similar to that of the local genotype. Together these trials suggest that forest managers have flexibility in managing loblolly pine stand density without altering wood properties. Furthermore, these results provide some evidence that moving genotypes may not carry a risk of reduced wood specific gravity.
Soil desiccation index under the different treatments.
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•Mongolian pine can create a serious imbalance between the water supply and demand.•Layers with a stable water level gradually ...disappear with increasing plantation age.•The effect of stand age on soil moisture was greater than planting density.•Stands must be thinned to a density of 333 trees ha−1 during the young stage.•Soil desiccation index under the different treatments.
Although the planting and the desertification control of Pinus sylvestris var. mongolica have long been explored, effect of the plantation density is still unclear, on the southwestern edge of the Mu Us Dunefield in northern China. This study investigated the soil moisture at five mineral soil depth from 2017 to 2018, and analyzed the effects of the trees on the soil moisture balance in plantations with different densities and ages. We found that the plantations changed water movement and storage in the aeolian sandy soil. Both stand age and density significantly affected the soil water content, but the effect of plantation age was greater than that of density. The soil water content decreased with increasing age, the thickness of the surface dry layer increased, and soil drying increased significantly. In the 4-year-old forests, soil moisture was adequate, and seasonal rainfall could partially compensate for the soil water deficit. In the 9-year-old forests, the water deficit was a serious concern at high tree densities, and seasonal rainfall did not compensate completely for the soil water deficit at densities greater than 400 trees ha−1, so the soil remained relatively dry at the end of the rainy season, even after more than 640 mm of rainfall. The 15- and 30-year-old forests experienced serious drought due to their drying effect on the soil. Overall, the trees promoted soil water loss, thereby creating a serious imbalance between the water supply and demand in this desert environment. High-density planting accelerated the deterioration of the water environment (i.e., soil drying) and threatened the future survival of the trees and other plants. Thus, ecological managers must reduce tree planting and test the effectiveness of reducing the density to 333 trees ha−1 during the young stage.
•Growth dominance increased from negative to positive with age in loblolly pine plantations.•More intensive silviculture decreased tree size inequality but increased growth dominance.•Higher planting ...densities increased both tree size inequality and growth dominance.•Row thinning treatments decreased both tree size inequality and growth dominance.•Stand biomass growth was negatively related to tree size inequality.•Stand biomass growth was positively related to growth dominance.
Understanding stand structure and growth relationships and how they are influenced by silvicultural treatments can help us optimize forest management regimes. With two large long-term silvicultural research experiments in loblolly pine plantations, we examined the effects of planting density, silvicultural intensity (sustained competition control and repeated fertilization), and thinning treatments on temporal patterns of stand biomass, biomass growth, tree size inequality, growth dominance, and on stand growth-structure relationships. Results showed that more intensive silvicultural treatments decreased tree size inequality but increased growth dominance, while higher planting densities increased both tree size inequality and growth dominance in unthinned plots. Growth dominance increased from negative to positive with age. For a given silviculture and planting density, tree size inequality became stable after 15 years while growth dominance continued to change over time. Thinning treatments decreased both tree size inequality and growth dominance, and there were no effects of silviculture and planting density in thinned stands. Stand biomass growth was negatively related to tree size inequality and positively related to growth dominance, after accounting for the effects of silvicultural treatment and planting density.
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