Introduction

Bamboos are woody plants that belong to subfamily Bambusosidee, family Graminaceae (or Poaceae), comprising approximately 1250–1500 species among 75–107 genera (Zhu 2001). They are spread over approximately 35 million hectares (M ha) of land, the equivalent of 0.9% of the total wooded area of the world (FAO 2020). Bamboos are broadly tolerant and adaptable to various climatic and edaphic conditions mainly in tropical and subtropical areas (Song et al. 2011). Most bamboo species are concentrated in China (4.8–5.7 M ha; Chen et al. 2009b) and India (15.7 M ha; FSI 2017), but others growing well in the temperate and mediterranean zones in Europe and North America (Canavan et al. 2017). Given the wide distribution of bamboos compared to other plant species and their high growth rate, bamboo-covered areas can sequester significant amounts of carbon (C), thus helping to mitigate the effects of climate change (Nath et al. 2015). However, some authors question the C sequestration potential of bamboo. For example, Liese (2009) and Düking et al. (2011) argues that the growth of new stems is simply a reallocation of carbohydrates from one part of the plant to the other because growth of the culm is not driven by photosynthesis but by energy produced by an older culm. Furthermore, given the relatively short lifespan of individual stalks (7–10 years), the stored C will potentially be released into the atmosphere relatively quickly, compared to the woody biomass of longer-lived tree species. However, harvested bamboo is often used to produce durable products such as furniture and building materials, which provides the equivalent to long-term C storage, offsetting the short lifespan of bamboo stalks (Huang et al. 2014). Bamboo can also produce phytolith-occluded C, a stable C form from decaying vegetation that remains in the soil for several thousand years (Huang et al. 2014). From the point of view of ecosystem functioning, the extensive fibrous rhizome and root system of bamboo can decrease surface soil erosion, reduce the risk of surface landslides, and stabilize riverbanks (Song et al. 2011). The fast -growing Moso bamboo [Phyllostachys edulis (Carrière) J. Houz., 1906] (Fu 2000) is widespread in China, representing about 70% of the total bamboo forest area (Wang et al. 2013). It is also planted in the Mediterranean region for wood, biomass and fiber production (Hakeem et al. 2015; Nayak and Mishra 2016; Boadu et al. 2022) and capturing atmospheric carbon dioxide (CO2). Recognized as equivalent to trees in the context of afforestation and reforestation (UNFCCC 2008), bamboos have also been certified under the verified carbon standard (FTFA 2012). Although C sequestration rates in Moso bamboo forests have been estimated in many studies (Zhou and Jiang 2004; Chen et al. 2009a; Wang et al. 2011; Yen and Lee 2011), the data varies greatly, perhaps from inconsistent calculations. Therefore, the C sequestration potential of Moso bamboo plantations needs to be determined more precisely to evaluate its potential in mitigating climate change, particularly outside Asia, where it is considered an invasive species.

Based on these premises, here we thus evaluated the carbon sequestration rates after a Moso bamboo replaced an annual cropland in the province of Viterbo in central Italy to gain a better understanding of the potential of Moso bamboo to mitigate climate change. We also addressed environmental concerns related to bamboo invasiveness in new areas of expansion.

Material and methods

Experimental sites

The study area, located on the Romolo Gentili farm in the municipality of Farnese (42′34′′5.52′′ N; 11°39′14.65′′ E) in Viterbo Province, Italy (Fig. 1), has a warm, temperate climate with an average temperature of 14.0 °C and 635 mm of annual rainfall. Summers are short, hot and dry; the long winters are very cold, and windy. The temperature during the year typically ranges from 1 to 30 °C and is rarely below −3 °C or above 35 °C. The prevalent soils of the area are Phaeozems as indicated on the soil map of the Lazio Region (Napoli et al. 2019). The investigated area includes a 6-ha cropland that historically has been cultivated with annual crops. In 2015, 4 ha of the cropland was planted with Moso bamboo, and the other 2 ha continued to be cultivated with 3-year rotation of barley, fallow, and herbage. Before the bamboo was planted, the soil was deeply plowed, and poultry manure was applied at about 1.5 Mg ha–1, then the soil was harrowed, and about 840 bamboo seedlings per hectare were manually planted in the field, and the soil surface in alternate rows was irrigated. An adjacent natural forest composed of turkey oak (Quercus cerris L. 1753) bordered both fields was also evaluated for its mitigation potential in comparison to that of the bamboo plantation.

Fig. 1
figure 1

a Location of the Farnese area in Italy. View of b the 2-ha sampling areas with indicated the plot position within the area and c 4-year-old Moso bamboo plantation

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Experimental design

In 2020, given the homogeneity of the area, an area of 2 ha (Fig. 1) was selected in the bamboo plantation, cropland and oak forest. Three 10 m by 10 m plots were randomly established in the bamboo plantation. Soil samples were collected at 0–15 cm and 15–30 cm depths at five random points in the corners and center of each plot by digging mini pits. A soil core was also collected in each mini pit (N = 5) by using cylinders of known volume to determine bulk density of the soil. The litter layer (N = 5) was collected within a 50 cm by 50 cm frame randomly placed in each plot. To measure the aboveground biomass (AGB), we cut three representative bamboo culms in each plot for each age class. Because the culms were removed the first year, only the culms of the last 3 years were present. Consequently, the number of culms for each age class was recorded within each plot. In the cropland, three plots 10 m by 10 m were also established, and samples were collected as done for the bamboo plantation. Based on the (2006) IPCC report, the AGB of the cropland was not measured, given that throughout the year all the C in the AGB is removed at harvest and no litter layer is present. For comparing the C stored in the bamboo plantation and cropland with the C stored in natural vegetation, three circular sampling plots (13-m radius) were also established in a forest adjacent to the bamboo and the cropland areas using the protocol of the National Forest Inventory (MIPAAF 2006). Within each circular plot, the height and DBH of each tree were measured, and soil samples and the litter layer were collected as done for the bamboo plantation and cropland plots. Deadwood was estimated along a transect of 26 m (e.g., the diameter of the plot) using the method of Alberti et al. (2008).

Estimation of C pools

The soil samples were taken to the laboratory and oven-dried (60 °C) to constant mass, except those for bulk density, which were oven-dried at 105 °C until constant mass. Once dried, all samples were sieved at 2 mm to separate fine soil particles (soil fraction < 2 mm) from rock fragments. The fine component from each sample was characterized for particle size distribution (e.g., pipette method) and pH using standardized methods (MIPAAF 2015). The SOC concentration in the fine particles was measured using the dry combustion method (Thermo-Finnigan Flash EA112 CHN, Okehampton, UK). The SOC stock was calculated as SOC stock = SOC × BD × Depth × [1 1 − (Rock fragment/100)], where SOC stock is the C stock (Mg C ha−1), SOC is the SOC concentration (g C kg−1); BD is the soil bulk density (Mg m−3); Depth is the soil layer sampled (cm), and Rock fragment is the correction factor for rock fragments (fraction > 2 mm) expressed in mass with respect to the fine soil particles (Poeplau et al. 2017).

The C in the litter layer, the culms, the leaves, and branches was analyzed by dry combustion (Thermo-Finnigan Flash EA112 CHN, Okehampton, UK) after the dried samples were ground using a ball mill and grinder. The AGB in the bamboo plantation was determined using the C concentration in the culms and culm dry mass.

The AGB of the trees in the forest plots was estimated using the allometric equations for turkey oak suggested by Tabacchi et al. (2011).

Because we did not collect samples to estimate wood density data, we estimated the volume of deadwood using the method of Harmon and Sexton (1996) and the volume of standing dead trees using the method of Alberti et al. (2008). The obtained values were converted into mass using species-specific wood density data (Global Wood Density Database 2015).

The belowground biomass was estimated using the root to shoot ratio of 0.42 for bamboo (Yuen et al. 2017) and of 0.20 for turkey oak (NIR 2023).

Statistical analyses

Using the methods of Blanco-Canqui et al. (2006), we applied a one-way ANOVA to test differences among the land uses for each C pool. We assumed a randomized experiment using the 15 sampling locations in each land-use as pseudoreplicates. Fisher’s protected least significant difference (LSD) method (P < 0.001) was used as post hoc test to compare means. All analyses were implemented using R 3.6.1 (R core Team 2020).

Results

Soil characterization and belowground C pools

The soil is classified as clay loam, and the soil particle distribution is relatively homogenous across the different sites; cropland on average has a lower sand and higher clay content than in the forest, but the differences are not significant (Table 1). The soil pH decreases from the cropland toward the forest, and differed significantly only when the forest soil is compared to the other sites. Bulk density increases with depth within each site but does not vary significantly among areas. Rock fragment content is also relatively stable and did no vary significantly across areas (Table 1).

Table 1 Mean ± SD values for physical and chemical properties of the soil at two depths at the three investigated sites
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SOC concentrations differed at each site, decreasing with increasing soil depth. At the 0–15-cm depth, significant differences were evident between areas; SOC increased from the annual cropland (18.1 ± 0.8 g C kg–1) to the forest (41.3 ± 2.3 g C kg−1), with intermediate values in the 4-year-old bamboo plantation (21.4 ± 1.6 g C kg–1). A similar trend was observed for the 15–30-cm depth: cropland (11.4 ± 0.7 g C kg–1), bamboo (12.3 ± 2.6 g C kg–1) and forest (32.5 ± 1.9 g C kg–1). The differences observed for the SOC concentrations were not reflected in the SOC stock in the different layers, and even considering the entire 0–30 cm soil depth, no significant differences were found between the cropland (33.2 ± 3.5 Mg C ha−1) and the bamboo plantation (40.7 ± 3.9 Mg C ha–1). The forest, however, stored significantly more SOC (55.8 ± 4.1 Mg C ha–1). The BGB component was 16.5 ± 2.3 Mg C ha–1 in the forest and 8.4 ± 1.9 Mg C ha–1 in the bamboo plantation.

Aboveground C pools

Based on the C analyses for the different compartments of the bamboo plantation (Table 2), all the aboveground C components were quantified. The total aboveground biomass of the bamboo plantation was 14.8 ± 1.8 Mg C ha–1, with culms contributing 80% and leaves and branches 20%. In terms of culms, those from the previous year contributed 45% to the total biomass (6.69 Mg C ha–1), those of 2 years for 35% (5.21 Mg C ha–1) and those of 3 years for 20% (2.98 Mg C ha–1). The AGB was much higher in the natural forest (78.5 ± 5.1 Mg C ha–1) than in the bamboo plantation, as it was the C stock in the litter layer of the forest (4.3 ± 0.9 Mg C ha–1) than in the bamboo plantation (1.8 ± 0.5 Mg C ha–1). The deadwood, present only in the forest, is 2.4 ± 0.7 Mg C ha–1 (Fig. 2).

Table 2 Carbon concentration in different compartments of Moso bamboo plants
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Fig. 2
figure 2

Ecosystem carbon stock at the three different sites (Mg C ha–1). Each histogram is divided into the five C pools, when present, with the aboveground C pools (aboveground biomass [AGB], deadwood, and litter) in the upper part of the graph and the belowground C pools (belowground biomass [BGB] and soil organic carbon [SOC]) in the lower part. Error bars are the standard deviation of the means for the respective whole aboveground and belowground components. Different lowercase letters indicate significant differences (P < 0.001, LSD test) among sites when comparing aboveground and belowground components separately. Different capital letters indicate significant differences (P < 0.001, LSD test) among sites at the ecosystem level

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Discussion

Carbon sequestration rate

The establishment of the Moso bamboo plantation on an annual cropland increased the C accumulation at the ecosystem level, particularly due to the AGB component. Considering that the culms are from only the last 3 years of the 4-yr-old bamboo plantation, the annual C sequestration rate in the AGB is 4.9 Mg C ha–1 a–1, which is however much lower than reported for the same type of bamboo in Southeast Asia. In fact, the highest C sequestration rates for a monopodial species were observed in Moso bamboo plantations in China (18 Mg C ha–1 a–1; He et al. 2007) and in Japan (13 Mg C ha–1 a–1; Isagi et al. 1993). Lower rates have been estimated in other studies. In a Moso bamboo forest in China, Yen and Lee (2011) estimated annual C sequestration to be 8.1 Mg C ha−1 a−1, while Xu et al. (2018) estimated 6.0 to 7.6 Mg C ha−1 a–1 in 36 bamboo forests along a latitudinal gradient. Although these values in China are much lower than the maximum C sequestration rate reported for Moso bamboo, they are still higher than our estimates for the plantation in Italy. The relatively low growth rate in our bamboo plantation compared to those in Southeast Asia might be related to the non-optimal climatic conditions, particularly the winter temperatures, which can influence the biomass growth by affecting the vitality of the culms (Xu et al. 2018). Zhou and Jiang (2004) and Kuehl et al. (2013) reported that the C sequestration rate for Moso bamboo biomass was 33% higher than that in a tropical mountain forest and 41% more than in a 5-year-old coniferous forest. Studies of natural forests from the Viterbo area have suggested sequestration rates of about 2 to 2.5 Mg C ha–1 a–1 for different Quercus species (Paganucci 1975; Quatrini et al. 2017), about 50% lower than the C sequestration rate of the Moso bamboo plantation. However, the rates for bamboo in Italy are not significantly different from those of some other fast-growing species in Italy such as black locust (Robinia pseudoacacia L) and black pine (Pinus nigra J.F. Arnold) with rates of 4 to 5 Mg C ha–1 a–1 (Nocentini and Puletti 2009; Quatrini et al. 2017). However, bamboo reaches maturity in terms of production between 7–8 years after its establishment; hence, the rates for the investigated plantation will likely increase in the following years. However, the lack of data for the Mediterranean environment makes it difficult to predict the amount of increase.

Among the few papers on SOC sequestration rates in bamboo, an annual increase in SOC of 0.59 Mg C ha–1 was reported for a bamboo-based agroforestry system in Northeast India (Nath et al. 2015). In our study, despite a small but significant difference in SOC concentration in the 0–15-cm layer between the annual cropland and the bamboo plantation, we found no difference in total SOC stock down to the 30-cm depth (Fig. 2). The fact that no soil C increase for bamboos was detected may be due to the high nutrient uptake by bamboos, which depletes soil nutrients and thus inhibits soil organic matter formation by bacteria. Such an impact of plants on soil C has been recently described by Chaplot (2021) and Chaplot and Smith (2023). For C stored at the ecosystem level, the land-use change from annual cropland to bamboo plantation allowed for a substantial removal of C from the atmosphere, about 9 Mg C ha–1 a–1.

Environmental concerns

The invasiveness and serious impact of Moso bamboo outside its range is well known and has been amply demonstrated in Japan (Xu et al. 2020), where its threat to biodiversity has been most evident to date. Equally well known is the impossibility of eradicating its extensive underground rhizomes because cutting them gives rise to new plants. Not only can bamboo invasion of forests greatly reduce plant biodiversity (Lima et al. 2012), it also can increase the risk of pathogen attack (Zhou 2006) and decrease animal biodiversity, particularly for birds (Yang et al. 2008). To regulate bamboo expansion, a possible solution is the use of plates to block root growth (Kitaoka et al. 2023). However, placement of the plate disturbs the soil, potentially leading to an increase in greenhouse gas emissions from the soil, which would decrease or negate the advantages from the C sequestered in the AGB biomass.

In addition, bamboo can affect soil microbial community composition but with contrasting effects: negative (Shen 2015), positive (Xu et al. 2015) or even neutral (Lin et al. 2014). All these aspects should be carefully considered before introducing the bamboo to a fragile environment such as the Mediterranean area, also considering the recent European Biodiversity Strategy 2030 (EC 2020), which is aimed at minimizing and, where possible, eliminating the introduction and establishment of possibly dangerous species in Europe.

Food security must also be considered before replacing croplands with bamboo plantations. Although bamboo is cultivated for its edible shoots in its area of origin, it is not currently embedded in the Mediterranean diet (Chandramouli and Viswanath 2015; Satya et al. 2012). Moreover, to achieve the growth rate and consequent C sequestration found in this study for bamboo Moso, higher levels of water and fertilizers are required than for the cereal-forage system practiced in the area (Lv et al. 2020). Therefore, the promising C mitigation potential offered by bamboo plantations might not be justified due to environmental and economic disadvantages of the intensive water and chemical use, especially considering the increasing water scarcity expected in the Mediterranean basin under future climate change.

Conclusion

This study, quantifying the impact of a bamboo plantation in a typical Mediterranean area, showed very promising results for sequestering C from the atmosphere. Nevertheless, ecological concerns related to the introduction of this species in an overexploited environment and recent EU regulations on biodiversity suggest that the species should not be grown outside its area of origin due to the risk of loss of biodiversity and endemic species.