PR | IFPRI3; ISI; CRP3.2; 4 Transforming Agricultural and Rural Economies | Development Strategies and Governance (DSG); Transformation Strategies | CGIAR Research Program on Maize (MAIZE)

The impact of ozone (O3) pollution events on the plant drought response needs special attention because spring O3 episodes are often followed by summer drought. By causing stomatal sluggishness, O3 could affect the stomatal dynamic during a subsequent drought event. In this context, we studied the impact of O3 exposure and water deficit (in the presence or in the absence of O3 episode) on the stomatal closure/opening mechanisms relative to irradiance or vapour pressure deficit (VPD) variation. Two genotypes of Populus nigra x deltoides were exposed to various treatments for 21 days. Saplings were exposed to 80 ppb/day O3 for 13 days, and then to moderate drought for 7 days. The curves of the stomatal response to irradiance and VPD changes were determined after 13 days of O3 exposure, and after 21 days in the case of subsequent water deficit, and then fitted using a sigmoidal model. The main responses under O3 exposure were stomatal closure and sluggishness, but the two genotypes showed contrasting responses. During stomatal closure induced by a change in irradiance, closure was slower for both genotypes. Nonetheless, the genotypes differed in stomatal opening under light. Carpaccio stomata opened more slowly than control stomata, whereas Robusta stomata tended to open faster. These effects could be of particular interest, as stomatal impairment was still present after O3 exposure and could result from imperfect recovery. Under water deficit alone, we observed slower stomatal closure in response to VPD and irradiance, but faster stomatal opening in response to irradiance, more marked in Carpaccio. Under the combined treatment, most of the parameters showed antagonistic responses. Our results highlight that it is important to take genotype-specific responses and interactive stress cross-talk into account to improve the prediction of stomatal conductance in response to various environmental modifications.

Drought characteristics (minimum flows, drought duration and volume deficit) of the Moraca river near Podgorica, Montenegro (Yugoslavia) are analyzed using the peaks over threshold method based on renewal processes. It is also shown that volume deficit and drought duration are highly correlated.

Withdrawal of water from surface water network should be concerned with preservation of the environment, meaning that the low flow regime in streams should be preserved within the range of natural regime. In order to formulate criteria for minimal allowed flows in streams, it was necessary to perform statistical analysis of low flows in rivers in Serbia (Yugoslavia). The criteria for water withdrawal are proposed on the basis of characteristic ratios between minimum and mean flows. Different criteria are proposed for cold and warm seasons.

Some weather events like drought, increased precipitation, and warming exert substantial impact on the terrestrial C and N cycling. However, it remains largely unclear about the effect of extreme weather events (extreme drought, heavy rainfall, extreme heat, and extreme cold) on terrestrial C and N cycling. This study aims to analyze the responses of pools and fluxes of C and N in plants, soil, and microbes to extreme weather events by conducting a global meta-analysis of 656 pairwise observations. Results showed that extreme weather events (extreme drought, heavy rainfall, and extreme heat) decreased plant biomass and C flux, and extreme drought and heavy rainfall decreased the plant N pool and soil N flux. These results suggest that extreme weather events weaken the C and N cycling process in terrestrial ecosystems. However, this study did not determine the impact of extreme cold on ecosystem C and N cycling. Additional field experiments are needed to reveal the effects of extreme cold on global C and N cycling patterns.

Dissolved inorganic nitrogen (DIN) is considered the main factor that induces eutrophication in water, and is readily influenced by hydrodynamic activities. In this study, a 4-year field investigation of nitrogen dynamics in a turbulent river was conducted, and a laboratory study was performed in the approximately homogeneous turbulence simulation system to investigate potential mechanisms involved in DIN transformation under turbulence. The field investigation revealed that, contrary to NO⁻₃ dynamics, the NH⁺₄ concentrations in water were lower in flood seasons than in drought seasons. Further laboratory results demonstrated that limitation of dissolved oxygen (DO) caused inactive nitrification and active denitrification in static river sediment. In contrast, the increased DO levels in turbulent river intensified the mineralization of organic nitrogen in sediment; moreover, ammonification and nitrification were activated, while denitrification was first activated and then depressed. Turbulence therefore decreased NH⁺₄ and NO⁻₂ concentrations, but increased NO⁻₃ and total DIN concentrations in the overlying water, causing the total DIN to increase from 0.4 mg/L to maximum of 1.0 and 1.7 mg/L at low and high turbulence, respectively. The DIN was maintained at 0.7 and 1.0 mg/L after the 30-day incubation under low and high turbulence intensities (ε) of 3.4 × 10⁻⁴ and 7.4 × 10⁻² m²/s³, respectively. These results highlight the critical role of DO in DIN budgets under hydrodynamic turbulence, and provide new insights into the DIN transport and transformation mechanisms in turbulent rivers.

Frequent drought events and particulate matter pollution from vehicular exhaust seriously affect urban plant growth and provisioning of ecological services. Yet, how plants respond physiologically and morphologically to these two combined stressors remains unknown. Here, we assessed particle retention dynamics and plant morphology and physiology of Euonymus japonicus Thunb. var. aurea-marginatus Hort. under continuous drought with severe exhaust exposure. Our results showed that continuous drought insignificantly lowered particle retention in each of three size fractions by 1.02 μg·cm⁻² on average in the first 28 days, but significantly lowered total particle retention by 35.75 μg·cm⁻² on the 35th day. We observed evident changes in morphology, leaf mass per area (LMA), pigments, gas exchange in all stressed plants. Compared with single stress, combined drought and pollution caused earlier yellowing and shedding of old leaves, significantly lowered LMA by 1.21 mg·cm⁻², caused a greater decline in pigments and net photosynthetic rate (Pₙ). Large particles may mainly explain pigment reduction, lower weekly LMA increases, and stomatal restriction, while coarse particles may be the main drivers of the decline in Pₙ. Continuous drought mediated the influence of all three particle sizes on some parameters, such as weakening the impact of total particles on LMA, strengthening the impact of fine particles on photosynthesis. Our findings suggest that drought accelerates the physiological responses of plants to exhaust pollution. Under controlled severe exhaust pollution conditions, the optimal time to maintain high particle retention during continuous drought without decline in physiological conditions for E. japonicus var. aurea-marginatus was 14 days. Some additional interventions after 14 days (it could be postponed appropriately under field conditions) may help ensure healthy growth of plants and retention of particulate matter.

Nitric oxide (NO) plays a critical role in atmospheric chemistry and also is a precursor of nitrate, which affects particle matter formation and nitrogen deposition. Agricultural soil has been recognized as a main source of atmospheric NO. However, quantifying the NO fluxes emitted from croplands remains a challenge and in situ long-term measurements of NO are still limited. In this study, we used an automated sampling system to measure NO fluxes with a high temporal resolution over two years (April 2017 to March 2019) from a rainfed maize field in the Northeast China. The cumulative annual NO emissions were 8.9 and 2.3 kg N ha⁻¹ in year 1 (April 2017 to March 2018) and year 2 (April 2018 to March 2019), respectively. These interannual differences were largely related to different weather conditions encountered. In year 1, a month-long drought before and after the seeding and fertilizing reduced plant N uptake and dramatically increased soil N concentration. The following moderate rainfalls promoted large amount of NO emissions, which remained high until late September. The NO fluxes in both years showed clearer seasonal patterns, being highest after fertilizer application in summer, and lowest in winter. The seasonal patterns of NO fluxes were mainly controlled by soil available N concentrations and soil temperatures. The contribution of NO fluxes during the spring freeze-thaw in both years was no more than 0.2% of the annual NO budget, indicating that the freeze-thaw effect on agricultural NO emissions was minimal. In addition, with high-resolution monitoring, we found that soil not only act as a NO source but also a sink. Long-term and high-resolution measurements help us better understand the diurnal, seasonal, and annual dynamics of NO emissions, build more accurate models and better estimate global NO budget and develop more effective policy responses to global climate change.

Soil nitrogen (N) leaching is recognized to have negative effects on the environment. There is a lack of studies on different simultaneously occurring drivers of environmental change, including changing rainfall and N deposition, on soil N leaching. In this study, a two factorial field experiment was conducted in a Korean pine forest with the following four treatments: 30% of throughfall reduction (TR), 50 kg N ha⁻¹ yr⁻¹ of N addition (N+), throughfall reduction plus N addition (TRN+) and natural forest (CK). The zero-tension pan lysimeter method was used to assess the response of soil N leaching loss to manipulated N addition and throughfall reduction. The results showed that the soil N leaching loss in natural forest was 5.0 ± 0.4 kg N ha⁻¹yr⁻¹, of which dissolved organic nitrogen (DON) accounted for 48%. Compared to natural forest, six years of N addition (NH₄NO₃, 50 kg N ha⁻¹ year⁻¹) significantly (P < 0.05) increased soil N leaching losses by 122%, especially in the form of NO₃⁻; a 30% reduction in throughfall slightly decreased N leaching losses by 23%; in combination, N addition and throughfall reduction increased N leaching losses by 48%. There was a strong interaction between N addition and throughfall reduction, which decreased N leaching loss by approximately 2.5 kg N ha⁻¹ yr⁻¹. Our results indicated that drought would diminish the enhancing effect of N deposition on soil N leaching. These findings highlight the importance of incorporating both N deposition and precipitation and their impacts on soil N leaching into future N budget assessments of forest ecosystems under global environmental change.