**2. Climatic effect**

CO2

ments [14].

The high absorption of CO2

148 Plant Ecology - Traditional Approaches to Recent Trends

biochemical, anatomical and morphological) [6].

consequences to the environment [11–13].

changes in C, N and P cycles [17].

appropriate proportions [19].

tion in adverse habitats [20].

account for 50% of plant dry mass [18].

considered to be 10–20, on a mass basis [22].

that will allow greater food security in the future.

concentrations induces changes in plants, especially in C3 plants, with an increase in the

may also lead to a gradual limitation of nutrients that can quickly

absorp‐

uptake of carbon (C), which may lead to a reduction of transpiration [2], because CO2

tion promotes stomata closure [3], which may limit the ability of plants to assimilate N [4].

limit the increase in plant production [5], because it affects the process of acclimatization that involves a series of changes in plant metabolism at different levels of organization (molecular,

In recent decades, anthropic activities have altered the P cycle; excessive doses of fertilizers are being used, thus inducing an increase in the input of this nutrient into terrestrial and aquatic ecosystems [7, 8]. Increased application of P may alter the balance between C, N and P in plants, and thus change the C:N:P stoichiometry ratios [8] and reduce the C:P ratio in plant tissues [9, 10]. Another concern is the change in N and P cycles, which can cause several

In this scenario, environmental responses of plants to global changes have a negative charac‐ ter with future losses to food production worldwide. Therefore, it is necessary to recognize the new stoichiometry (C:N:P ratios) that occurs in plants in this new scenario in order to try to identify a plant‐environment interaction that may allow an increase in food production and

The interactions that occur between elements are complex and their effects reflect the mineral composition of plants. An alternative to study the multiple ratios between elements in a plant is to focus on stoichiometric ratios that are considered to be an important biological indicator for elucidating plant responses to various changes and their adaptation to different environ‐

Moreover, the study of plant stoichiometry can influence ecological processes, and thus modulate the structure and function of the ecosystem [15, 16]. It can also effectively indicate

The carbon (C):nitrogen (N):phosphorus (P) ratio is one of the most investigated topics in stoichiometry, because N and P limit plant growth and C is the structural basis of plants: they

These elements are strongly linked to the biochemical functioning of plants. P is an important element in the production of ribosomes; it is involved in the synthesis of proteins containing N and C. There are, therefore, fundamental biochemical reasons for using these elements in

In plants, C:N and C:P ratios represent the ability of photosynthetic fixation of C through N or P accumulation. Also, the N:P ratio can be used as an indicator to study plant nutrient limita‐

Therefore, the proportions of leaf N and P in plant biomass can be an indicator of vegeta‐ tion composition and nutrient limitation at the community level [21, 22]. An N:P < 14 ratio indicates N limitation, whereas an index >16 suggests P limitation [21]. An ideal N:P ratio is The climate exerts a strong control on plant growth and hence it influences plant stoichiom‐ etry. Changes in growth rate can be caused by changes in the availability of elements as a result of changes in temperature, latitude, drought and warming. Thus, one of the challenges in the future should elucidate the reasons and implications of this variability which may alter the success of resident plant species.

### **2.1. Latitude**

Latitude is a climatic parameter that can influence stoichiometric ratios. In this scenario, three analyses of leaf N:P patterns indicated that the N:P ratio is approximately half when latitude in the Equator is 70° (**Figure 1**) [23, 24].

The reason for this trend can be explained by N concentrations (N:C) which are approxi‐ mately constant for latitudes, increasing P concentrations as latitude changes. This is indica‐ tive of a trend in N:P [23].

A study that analysed foliar N:P ratio as a function of latitude showed that this ratio increases with temperature [25]. This increase in temperature towards the Equator occurs because P is

**Figure 1.** Variation in N:P (molar ratio) in foliage (open triangles) and litter (solid diamonds) as a function of latitude [23].

an important limiting nutrient in tropical soils and N is the main limiting nutrient in temper‐ ate regions and high‐latitude soils.

### **2.2. Light**

Differences in the exposure of plants to sunlight can also affect their stoichiometry. One study compared the N:P ratio of sunlight‐exposed leaves and shade‐exposed leaves of two species of *Quercus ilex* and *Quercus coccifera* plants in Spain [26]. In both species, the sunlight‐exposed leaves had about twice as much concentration of P compared with the shade‐exposed leaves, while there were minor differences in the concentrations of N. The P:N ratio was also higher in the sunlight‐exposed leaves than in the shade‐exposed ones.

This result indicates that the two plant species may show ability to adequately respond to changes in environmental factors by means of phenotypic plasticity, which is positively related to the ecological distribution of species.

### **2.3. Drought**

Long periods of water stress often cause a reduction in plant growth [27], but plants respond with increased absorption of water and improved mechanisms for water use efficiency. The events caused by water stress initiate physiological responses in plants which often affect ecosystems and nutrient cycling [28, 29].

Mathematical models predict an increase in water deficit in various areas of the world. The effects of increased water deficit differ across ecosystems and species. In semi‐arid areas, drought reduces the C:N ratio in the roots of the species *Quercus ilex* [30, 31].

In other plant species, drought increased the C:N and C:P ratios of leaves of shrubs and trees in the Mediterranean, as a result of protection mechanisms [32, 33] associated with the pres‐ ence of leaves whose structure is drought‐tolerant [34].

In moist temperate ecosystems, the C:N ratio can decrease moderately because plants increase the uptake of N and reduce their growth [35].

Thus, evidence suggests that drought tends to increase C:N ratios of photosynthetic tissue in semi‐arid environments, but the effects are not so clear in moist ecosystems (**Figure 2**), in which drought may affect various aspects of plants.

In dry regions, the increase in C:N ratios can combine with increases in response to CO2 con‐ centrations, which suggests synergy that increases the C:N ratio (and, probably, the C:P ratio) and slows the N and P cycles, thus reducing the availability of N and P and their concentra‐ tions in the biomass [32, 36].

### **2.4. Warming**

The increase in ambient temperature can increase the mineralization of organic C and, thus, increase the amount of atmospheric CO2 [37]. This may explain why several studies have not detected an effect of high ambient temperatures on the C:N ratios of some plants (**Figure 2**).

Ecological Response to Global Change: Changes in C:N:P Stoichiometry in Environmental... http://dx.doi.org/10.5772/intechopen.69246 151

an important limiting nutrient in tropical soils and N is the main limiting nutrient in temper‐

Differences in the exposure of plants to sunlight can also affect their stoichiometry. One study compared the N:P ratio of sunlight‐exposed leaves and shade‐exposed leaves of two species of *Quercus ilex* and *Quercus coccifera* plants in Spain [26]. In both species, the sunlight‐exposed leaves had about twice as much concentration of P compared with the shade‐exposed leaves, while there were minor differences in the concentrations of N. The P:N ratio was also higher

This result indicates that the two plant species may show ability to adequately respond to changes in environmental factors by means of phenotypic plasticity, which is positively

Long periods of water stress often cause a reduction in plant growth [27], but plants respond with increased absorption of water and improved mechanisms for water use efficiency. The events caused by water stress initiate physiological responses in plants which often affect

Mathematical models predict an increase in water deficit in various areas of the world. The effects of increased water deficit differ across ecosystems and species. In semi‐arid areas,

In other plant species, drought increased the C:N and C:P ratios of leaves of shrubs and trees in the Mediterranean, as a result of protection mechanisms [32, 33] associated with the pres‐

In moist temperate ecosystems, the C:N ratio can decrease moderately because plants increase

Thus, evidence suggests that drought tends to increase C:N ratios of photosynthetic tissue in semi‐arid environments, but the effects are not so clear in moist ecosystems (**Figure 2**), in

centrations, which suggests synergy that increases the C:N ratio (and, probably, the C:P ratio) and slows the N and P cycles, thus reducing the availability of N and P and their concentra‐

The increase in ambient temperature can increase the mineralization of organic C and, thus,

detected an effect of high ambient temperatures on the C:N ratios of some plants (**Figure 2**).

[37]. This may explain why several studies have not

con‐

In dry regions, the increase in C:N ratios can combine with increases in response to CO2

drought reduces the C:N ratio in the roots of the species *Quercus ilex* [30, 31].

in the sunlight‐exposed leaves than in the shade‐exposed ones.

related to the ecological distribution of species.

ecosystems and nutrient cycling [28, 29].

ence of leaves whose structure is drought‐tolerant [34].

the uptake of N and reduce their growth [35].

tions in the biomass [32, 36].

increase the amount of atmospheric CO2

**2.4. Warming**

which drought may affect various aspects of plants.

ate regions and high‐latitude soils.

150 Plant Ecology - Traditional Approaches to Recent Trends

**2.2. Light**

**2.3. Drought**

**Figure 2.** Reported increases, decreases and absence of change in C:N and N:P ratios in response to warming or drought [13].

Plant respiratory responses to warming may affect the availability of light, water and CO<sup>2</sup> , and plant responses may differ across species and organs [38]. Thus, evidence suggests that the rise in temperature predicted by climate models will increase the C:N and C:P ratios of plants based on mechanisms of water stress resistance or water‐use efficiency. This increase of C:N and C:P ratios caused by warming coincides in semi‐arid regions.

In cold ecosystems that are not limited by water, the effects of warming on C:N ratios of plants are not well understood. However, some studies have shown that warming has changed the C:N ratios of plants, increasing production capacity and nutrient absorption of plants [39]. Other studies in pastures in cold regions have not found any effects [40] or have reported an increase in the C:N ratio associated with an effect of dilution by an increase in biomass production [41].
