Ecological Impacts of Rainfall Regimes Changes on Agroecosystems in Southern of South America

Changing climate affects ecosystems in a variety of ways. As each species responds to its changing environment, its interactions with the physical world and the organisms around it change too. This A significant attention is paid to how changes in seasonal and annual precipitation sums affect ecosystems. Argentina does not escape the phenomenon of global climate change, in which numerous local references have reported the change rainfall patterns in different regions within the country. Studies that have not yet been published for the province of Entre Ríos (Argentina) are being carried out, which have allowed to demonstrate a change in the variation of monthly, seasonal and annual rainfall. The partial results confirm a sustainable increase in annual precipitation, with the 1970s being a significant breaking point. These changes have caused easily observable modifications in some of the components of ecosystems, for example: the soil and vegetation. In this manuscript the effects of climate change and a case study corresponding to typical agroecosystems of southern South America were presented. In a climate change scenario, local information is crucial to understand what the magnitude is and how the effects can be mitigated.


Copyright © Sabattini Julian Alberto
MCDA.000646. 6(5).2020 impact may lead to dramatic ecological changes [1]. For instance, climate change may exacerbate the stress that land development places on fragile coastal areas. Additionally, recently logged forested areas may become vulnerable to erosion if climate change leads to increases in heavy rain storms.
Ecosystems can serve as natural buffers from extreme events such as wildfires, flooding, and drought. Climate change and human modification may restrict ecosystems ability to temper the impacts of extreme conditions, and thus may increase vulnerability to damage. Examples include reefs and barrier islands that protect coastal ecosystems from storm surges, wetland ecosystems that absorb floodwaters, and cyclical wildfires that clear excess forest debris and reduce the risk of dangerously large fires [2]. In some cases, ecosystem change occurs rapidly and irreversibly because a threshold, or "tipping point", is passed. The extreme climate-related events in the South America region varies considerably due to the range of climate regimes in the region. Shifting temporal and spatial patterns of rainfall are key drivers of risk in Southern of South America. The El Niño-Southern Oscillation (ENSO) is main driver of current interannual climate variability in that region, contributing to the substantial spatial and temporal variation in extreme climate-related events. El Niño is typically associated with drier than normal conditions, and La Niña with wetter conditions. In South America, El Niño have been associated will flooding conditions, mainly the Pampas areas in Argentina. Although ENSO will remain the dominant mode of interannual variability in the future, the increased moisture availability in the atmosphere associated with climate change will likely result in the intensification of related rainfall.
Global warming affects the hydrological cycle over land, resulting in observed changes to precipitation frequency, intensity, duration and amount [3,4]. Although significant attention is paid to how changes in seasonal and annual precipitation sums affect ecosystems, relatively less is known about the ecological impacts of heavy rainfall events, which are being observed with increasing frequency and severity and are expected to increase in the future [4][5][6]. Argentina does not escape the phenomenon of global climate change, in which numerous local references have reported its effects in different regions within the country. However, we are going to make a mention of the central region of Argentina, where according to Köppen, it is characterized by a humid subtropical climate.
Considering the temperature, summers are hot and humid, while winters are cool. On the other hand, rainfall is abundant in coastal areas, which decrease during a less and less humid winter as the distance from the coast increases. Those of winter are associated with storms from the west winds that run from west to east, and many summer rains occur during storm fronts that eventually cause tropical storms, registering in recent years numerous tornadoes that were not frequent. The most important agricultural activity in South America is concentrated in this region, presenting numer-ous agroecosystems such as the production of cereals (wheat, corn, sorghum), oilseeds (soybeans, sunflowers), extensive and intensive cattle farming (feedlot), among other systems less relevant productive. There they optimize the most important ecological factors that make it possible to obtain the highest productivity from these agroecosystems: the soil, the climate (particularly the seasonality of temperature and precipitation), the altitude above sea level, and the appropriate application of management techniques suitable.

Case of study: Entre Ríos, Argentina
In the last decade, a substantial change in the average climate as confirmed by reports from the region (Proyecto SIBER, Bolsa de Cereales de Entre Ríos). These hypotheses and statements are consistent with other research carried out. Rainfall changes may reduce long-term productive capacity of soil because of nutrient loss [7,8]. Collectively, these studies demonstrate how the temporal pattern and event size of precipitation and resulting soil moisture regime represent an important knowledge gap. Recent studies suggest that heavy rainfall caused even greater negative effects on grass reproduction and wheat yield than extreme drought [8,9], which is often presumed to have the strongest and most widespread effects on terrestrial ecosystems [10,11]. However, except for these limited examples, little is known about heavy rainfall impacts across multiple hierarchical levels from individual plants to the ecosystem scale.
Moreover, effects have been observed in the temperate natural grasslands of southern South America, particularly those that make up the typical native forests of the region [12,13]. Natural grasslands are the most important forage supply in bovine farming systems. These present a growth peak that normally occurs in spring and autumn, due to the composition of the plant species that compose it, mainly C3 species. In this sense, the normal tempera- These qualitative results have not only been observed in herbaceous vegetation, but also in the shrub layer. The rainfall regimes, fundamentally, have caused the invasion of shrub species to advance, generating interspecific competition for light, water and nutrients with the herbaceous species that are consumed by cattle, sheep and horses in the mentioned region [12]. In addition, the Previous studies based on precipitation gradients across multiple sites or a long temporal scale at a single site usually report positive relationships of precipitation with gross ecosystem CO2 uptake or aboveground net primary productivity. Ecosystem benefits from increased precipitation manifest in changes across hierarchical levels, including increased metabolism (e.g. leaf photosynthesis) [16,17], improvement of soil nutrient availability [18], and resultant changes in community composition [19]. However, variability in precipitation totals over seasonal to annual scales is very different from altered incidence of heavy rainfall events, with large cumulative depths occurring over multiple consecutive days. Ecological responses to precipitation change may vary over time and depend on the persistence or recurrence of the change [17]. Plants might form 'stress memory' in physiology after a stress experience (e.g. drought), which may stabilize ecosystems; that is, ecosystems tend to remain stable when faced with climate stress if the ecosystem has previously experienced a similar stress [20,21]. Moreover, a plant may alter its morphological traits to survive under extreme water conditions, such as through changes in root: shoot ratio [22] or root and leaf structure [23]. Such an adaptation in morphology may increase an individual's tolerance to subsequent extreme conditions [24]. Therefore, it seems logical to hypothesize that responses of ecosystem structure and function to repeated (i.e. annually) heavy rainfall would change over time. However, to date, most heavy rainfall results are from opportunistic studies of events that occurred naturally without repetition (Smith, 2011). These studies are usually too short (1 or 2 yr) to establish a clear trajectory of change with time. As a consequence, ecological responses to recurrent heavy rainfall remain unclear.
Another aspect to consider is the impact on animals, in this case we can mention insects. Insect populations are particularly responsive to climate change because of their sensitivity to temperature, short generation times, and high flight capacity. Observations of insect herbivory on an oak lineage during Quaternary climate change indicate that there was higher damage during warm and wet periods [25]. In recent years, the magnitude and severity of epidemics have increased, with outbreak populations expanding to northern and high-elevation areas, where in the past, such disturbances were relatively rare [26][27][28][29]. Forest insect outbreaks are major disturbances by native or non-native insects, as they can be synchronous over large geographic areas and cause region-wide mortality of host trees in a relatively short period of time [26,[28][29][30]. Disturbance due to forest insects have been recorded to increase land surface temperature and cause declines in gross primary productivity [31,32].
A local example that deserves to be studied in more detail is the relationship and possible effects between the historical changes in rainfall and the founding of new colonies of leafcutting ants. If we make a qualitative association with the results obtained in the mentioned area, we can modify the behavior of the reproductive cycles of leaf cutter ants, particularly those of the Atta genus [33]. Residents frequently mention that in recent years a significant advance has been observed in the number of nests of these ants. This can be attributed to a better soil moisture condition after the nuptial flight, guaranteeing better digging conditions and development of the initial chamber [34,35]. However, they are hypotheses that should be tested in a timely manner.